doc: kernel: define additional doxygen groups

Some groups are used by multiple files/tests, define them globally in
doc/

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

doc/_doxygen/groups.dox

@@ -79,4 +79,14 @@
 @{
 @}
 
+@brief Tests
+@defgroup all_tests Tests
+@{
+@}
+
+@defgroup kernel_memprotect_tests Memory Protection
+@ingroup all_tests
+@{
+@}
+
 */

tests/kernel/mem_protect/mem_protect/src/mem_partition.c

@@ -7,6 +7,8 @@
 #include <zephyr/kernel.h>
 #include "mem_protect.h"
 
+
+
 /* Add volatile to disable pre-calculation in compile stage in some
  * toolchain, such as arcmwdt toolchain.
  */