drm/vkms: Add support for DRM_FORMAT_R*

drm/vkms: Add support for DRM_FORMAT_R*

This add the support for:
- R1/R2/R4/R8

R1 format was tested with [1] and [2].

[1]: https://lore.kernel.org/r/20240313-new_rotation-v2-0-6230fd5cae59@bootlin.com
[2]: https://lore.kernel.org/igt-dev/20240306-b4-kms_tests-v1-0-8fe451efd2ac@bootlin.com/

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250415-yuv-v18-8-f2918f71ec4b@bootlin.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>