drm/selftests: Move i915 buddy selftests into drm

- move i915 buddy selftests into drm selftests folder
- add Makefile and Kconfig support
- add sanitycheck testcase

Prerequisites
- These series of selftests patches are created on top of
  drm buddy series
- Enable kselftests for DRM as a module in .config

Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220222174845.2175-1-Arunpravin.PaneerSelvam@amd.com


Signed-off-by: Christian König <christian.koenig@amd.com>