doc: Create dox file for tests

Create top level doxygen groups to be used by tests and move to
dedidcated dox file for tests.

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

Author: nashif

doc/_doxygen/groups.dox

@@ -85,14 +85,4 @@
 @{
 @}
 
-@brief Tests
-@defgroup all_tests Tests
-@{
-@}
-
-@defgroup kernel_memprotect_tests Memory Protection
-@ingroup all_tests
-@{
-@}
-
 */

tests/tests.dox

@@ -0,0 +1,18 @@
+/**
+
+@brief Tests
+@defgroup all_tests Tests
+@{
+@}
+
+@defgroup kernel_fatal_tests Fatal Handling
+@ingroup all_tests
+@{
+@}
+
+@defgroup kernel_memprotect_tests Memory Protection
+@ingroup all_tests
+@{
+@}
+
+*/