kernel: add memory domain APIs

Add the following application-facing memory domain APIs:

k_mem_domain_init() - to initialize a memory domain
k_mem_domain_destroy() - to destroy a memory domain
k_mem_domain_add_partition() - to add a partition into a domain
k_mem_domain_remove_partition() - to remove a partition from a domain
k_mem_domain_add_thread() - to add a thread into a domain
k_mem_domain_remove_thread() - to remove a thread from a domain

A memory domain would contain some number of memory partitions.
A memory partition is a memory region (might be RAM, peripheral
registers, flash...) with specific attributes (access permission,
e.g. privileged read/write, unprivileged read-only, execute never...).
Memory partitions would be defined by set of MPU regions or MMU tables
underneath.
A thread could only belong to a single memory domain any point in time
but a memory domain could contain multiple threads.
Threads in the same memory domain would have the same access permission
to the memory partitions belong to the memory domain.

The memory domain APIs are used by unprivileged threads to share data
to the threads in the same memory and protect sensitive data from
threads outside their domain. It is not only for improving the security
but also useful for debugging (unexpected access would cause exception).

Jira: ZEP-2281

Signed-off-by: Chunlin Han <chunlin.han@linaro.org>

arch/arm/core/swap.S

@@ -175,6 +175,14 @@ _thread_irq_disabled:
     pop {r2, lr}
 #endif /* CONFIG_MPU_STACK_GUARD */
 
+#ifdef CONFIG_USERSPACE
+    /* r2 contains k_thread */
+    add r0, r2, #0
+    push {r2, lr}
+    blx configure_mpu_mem_domain
+    pop {r2, lr}
+#endif /* CONFIG_USERSPACE */
+
     /* load callee-saved + psp from thread */
     add r0, r2, #_thread_offset_to_callee_saved
     ldmia r0, {v1-v8, ip}