drm/vkms: Create helper macro for YUV formats

drm/vkms: Create helper macro for YUV formats

The callback functions for line conversion are almost identical for
semi-planar formats. The generic READ_LINE_YUV_SEMIPLANAR macro
generate all the required boilerplate to process a line from a
semi-planar format.

Reviewed-by: Maíra Canal <mcanal@igalia.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Link: https://lore.kernel.org/r/20250703-b4-new-color-formats-v7-7-15fd8fd2e15c@bootlin.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>