tests: add more test descriptions

Add more test descriptions based on exiting comments.

Signed-off-by: Thomas Wood <thomas.wood@intel.com>

tests/gem_threaded_access_tiled.c

@@ -34,6 +34,8 @@
 #include "ioctl_wrappers.h"
 #include "intel_bufmgr.h"
 
+IGT_TEST_DESCRIPTION("Check parallel access to tiled memory.");
+
 /* Testcase: check parallel access to tiled memory
  *
  * Parallel access to tiled memory caused sigbus