doc: doxygen: add @brief to few APIs

Add some clarity to some of the groups using @brief.

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

Author: nashif

include/zephyr/arch/arch_interface.h

@@ -1259,6 +1259,7 @@ void arch_spin_relax(void);
 /**
  * @defgroup arch-stackwalk Architecture-specific Stack Walk APIs
  * @ingroup arch-interface
+ * @brief Architecture-specific Stack Walk APIs
  *
  * To add API support to an architecture, `arch_stack_walk()` should be implemented and a non-user
  * configurable Kconfig `ARCH_HAS_STACKWALK` that is default to `y` should be created in the

include/zephyr/kernel.h

@@ -5801,6 +5801,7 @@ void k_heap_free(struct k_heap *h, void *mem) __attribute_nonnull(1);
 
 /**
  * @defgroup heap_apis Heap APIs
+ * @brief Memory allocation from the Heap
  * @ingroup kernel_apis
  * @{
  */
@@ -5958,6 +5959,8 @@ enum _poll_states_bits {
 
 /**
  * @defgroup poll_apis Async polling APIs
+ * @brief An API to wait concurrently for any one of multiple conditions to be
+ *        fulfilled
  * @ingroup kernel_apis
  * @{
  */

include/zephyr/kernel_version.h

@@ -18,6 +18,8 @@ extern "C" {
  * @ingroup kernel_apis
  * @{
  *
+ * @brief Kernel Version APIs
+ *
  * The kernel version has been converted from a string to a four-byte
  * quantity that is divided into two parts.
  *