doc: add kernel version API to doxygen

Put kernel version API into doxygen and make it available as a
documented API.

Fixes #6319

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

doc/api/kernel_api.rst

@@ -241,6 +241,14 @@ of variable-size data items.
    :project: Zephyr
    :content-only:
 
+Kernel Version
+**************
+Kernel version handling and APIs related to kernel version being used.
+
+.. doxygengroup:: version_apis
+   :project: Zephyr
+   :content-only:
+
 Memory Domain
 *************
 

include/kernel_version.h

@@ -13,7 +13,11 @@
 extern "C" {
 #endif
 
-/*
+/**
+ * @defgroup version_apis Version APIs
+ * @ingroup kernel_apis
+ * @{
+ *
  * The kernel version has been converted from a string to a four-byte
  * quantity that is divided into two parts.
  *
@@ -32,8 +36,20 @@ extern "C" {
 
 /* kernel version routines */
 
+/**
+ * @brief Return the kernel version of the present build
+ *
+ * The kernel version is a four-byte value, whose format is described in the
+ * file "kernel_version.h".
+ *
+ * @return kernel version
+ */
 extern u32_t sys_kernel_version_get(void);
 
+/**
+ * @}
+ */
+
 #ifdef __cplusplus
 }
 #endif

kernel/version.c

@@ -1,5 +1,3 @@
-/* version.c */
-
 /*
  * Copyright (c) 1997-2010, 2012-2014 Wind River Systems, Inc.
  *
@@ -10,7 +8,6 @@
 #include "version.h" /* generated by MAKE, at compile time */
 
 /**
- *
  * @brief Return the kernel version of the present build
  *
  * The kernel version is a four-byte value, whose format is described in the