drm/selftests: add drm buddy alloc limit testcase

drm/selftests: add drm buddy alloc limit testcase

add a test to check the maximum allocation limit

v2(Matthew Auld):
  - added err = -EINVAL in block NULL check
  - removed unnecessary test succeeded print

Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@amd.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220222174845.2175-2-Arunpravin.PaneerSelvam@amd.com
Signed-off-by: Christian König <christian.koenig@amd.com>