drm/i915/display: Indexed 8bit format does not support async flip

Async flip is not supported with Indexed 8 bit format as it depends on
LUT and can't be updated atomically.

Note: This may change the alignment for C8 framebuffers on some
platforms.

Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/20250407-asyn-v13-5-b93ef83076c5@intel.com