headers: Refactor kernel and arch headers.

This commit refactors kernel and arch headers to establish a boundary
between private and public interface headers.

The refactoring strategy used in this commit is detailed in the issue

This commit introduces the following major changes:

1. Establish a clear boundary between private and public headers by
  removing "kernel/include" and "arch/*/include" from the global
  include paths. Ideally, only kernel/ and arch/*/ source files should
  reference the headers in these directories. If these headers must be
  used by a component, these include paths shall be manually added to
  the CMakeLists.txt file of the component. This is intended to
  discourage applications from including private kernel and arch
  headers either knowingly and unknowingly.

  - kernel/include/ (PRIVATE)
    This directory contains the private headers that provide private
   kernel definitions which should not be visible outside the kernel
   and arch source code. All public kernel definitions must be added
   to an appropriate header located under include/.

  - arch/*/include/ (PRIVATE)
    This directory contains the private headers that provide private
   architecture-specific definitions which should not be visible
   outside the arch and kernel source code. All public architecture-
   specific definitions must be added to an appropriate header located
   under include/arch/*/.

  - include/ AND include/sys/ (PUBLIC)
    This directory contains the public headers that provide public
   kernel definitions which can be referenced by both kernel and
   application code.

  - include/arch/*/ (PUBLIC)
    This directory contains the public headers that provide public
   architecture-specific definitions which can be referenced by both
   kernel and application code.

2. Split arch_interface.h into "kernel-to-arch interface" and "public
  arch interface" divisions.

  - kernel/include/kernel_arch_interface.h
    * provides private "kernel-to-arch interface" definition.
    * includes arch/*/include/kernel_arch_func.h to ensure that the
     interface function implementations are always available.
    * includes sys/arch_interface.h so that public arch interface
     definitions are automatically included when including this file.

  - arch/*/include/kernel_arch_func.h
    * provides architecture-specific "kernel-to-arch interface"
     implementation.
    * only the functions that will be used in kernel and arch source
     files are defined here.

  - include/sys/arch_interface.h
    * provides "public arch interface" definition.
    * includes include/arch/arch_inlines.h to ensure that the
     architecture-specific public inline interface function
     implementations are always available.

  - include/arch/arch_inlines.h
    * includes architecture-specific arch_inlines.h in
     include/arch/*/arch_inline.h.

  - include/arch/*/arch_inline.h
    * provides architecture-specific "public arch interface" inline
     function implementation.
    * supersedes include/sys/arch_inline.h.

3. Refactor kernel and the existing architecture implementations.

  - Remove circular dependency of kernel and arch headers. The
   following general rules should be observed:

    * Never include any private headers from public headers
    * Never include kernel_internal.h in kernel_arch_data.h
    * Always include kernel_arch_data.h from kernel_arch_func.h
    * Never include kernel.h from kernel_struct.h either directly or
     indirectly. Only add the kernel structures that must be referenced
     from public arch headers in this file.

  - Relocate syscall_handler.h to include/ so it can be used in the
   public code. This is necessary because many user-mode public codes
   reference the functions defined in this header.

  - Relocate kernel_arch_thread.h to include/arch/*/thread.h. This is
   necessary to provide architecture-specific thread definition for
   'struct k_thread' in kernel.h.

  - Remove any private header dependencies from public headers using
   the following methods:

    * If dependency is not required, simply omit
    * If dependency is required,
      - Relocate a portion of the required dependencies from the
       private header to an appropriate public header OR
      - Relocate the required private header to make it public.

This commit supersedes #20047, addresses #19666, and fixes #3056.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

include/timeout_q.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2015 Wind River Systems, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_KERNEL_INCLUDE_TIMEOUT_Q_H_
+#define ZEPHYR_KERNEL_INCLUDE_TIMEOUT_Q_H_
+
+/**
+ * @file
+ * @brief timeout queue for threads on kernel objects
+ */
+
+#include <kernel.h>
+
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef CONFIG_SYS_CLOCK_EXISTS
+
+static inline void z_init_timeout(struct _timeout *t)
+{
+	sys_dnode_init(&t->node);
+}
+
+void z_add_timeout(struct _timeout *to, _timeout_func_t fn, s32_t ticks);
+
+int z_abort_timeout(struct _timeout *to);
+
+static inline bool z_is_inactive_timeout(struct _timeout *t)
+{
+	return !sys_dnode_is_linked(&t->node);
+}
+
+static inline void z_init_thread_timeout(struct _thread_base *thread_base)
+{
+	z_init_timeout(&thread_base->timeout);
+}
+
+extern void z_thread_timeout(struct _timeout *to);
+
+static inline void z_add_thread_timeout(struct k_thread *th, s32_t ticks)
+{
+	z_add_timeout(&th->base.timeout, z_thread_timeout, ticks);
+}
+
+static inline int z_abort_thread_timeout(struct k_thread *thread)
+{
+	return z_abort_timeout(&thread->base.timeout);
+}
+
+s32_t z_get_next_timeout_expiry(void);
+
+void z_set_timeout_expiry(s32_t ticks, bool idle);
+
+s32_t z_timeout_remaining(struct _timeout *timeout);
+
+#else
+
+/* Stubs when !CONFIG_SYS_CLOCK_EXISTS */
+#define z_init_thread_timeout(t) do {} while (false)
+#define z_add_thread_timeout(th, to) do {} while (false && (void *)to && (void *)th)
+#define z_abort_thread_timeout(t) (0)
+#define z_is_inactive_timeout(t) 0
+#define z_get_next_timeout_expiry() (K_FOREVER)
+#define z_set_timeout_expiry(t, i) do {} while (false)
+
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_KERNEL_INCLUDE_TIMEOUT_Q_H_ */