tests: DRM selftests: switch to KUnit

As the DRM selftests are now using KUnit [1], update IGT tests as well.

[1] - https://lore.kernel.org/all/20220708203052.236290-1-maira.canal@usp.br/



Signed-off-by: Isabella Basso <isabbasso@riseup.net>

v1 -> v2:
- drm_buddy|drm_mm: fallback to igt_kselftests if igt_kunit failed
  with code other than IGT_EXIT_ABORT
- kms_selftest: move igt_kunit tests to separate subtests
- kms_selftest: fallback to igt_kselftests if all subtests failed

v2 -> v3:
- expose all subtests

Signed-off-by: Dominik Karol Piątkowski <dominik.karol.piatkowski@intel.com>
Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>