drm/selftests: add drm buddy alloc range testcase

drm/selftests: add drm buddy alloc range testcase

- add a test to check the range allocation
- export get_buddy() function in drm_buddy.c
- export drm_prandom_u32_max_state() in lib/drm_random.c
- include helper functions
- include prime number header file

v2:
  - add drm_get_buddy() function description (Matthew Auld)
  - 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/20220222174845.2175-3-Arunpravin.PaneerSelvam@amd.com
Signed-off-by: Christian König <christian.koenig@amd.com>