drm/connector: Introduce drm_output_color_format enum

drm/connector: Introduce drm_output_color_format enum

The EDID parsing code initially introduced the DRM_COLOR_FORMAT_*
defines to represent the sink capabilities. Since a given sink could
support multiple formats, it was first defined as a bitmask.

However, the core and drivers have since leveraged those defines to
represent both the supported formats but also the current format being
used.

Considering the latter case, the more natural, and consistent, thing to
do would be to create an enum of all the possible formats, and then list
the supported formats using a bitmask of the individual enum values.

Let's create a new enum following that pattern, drm_output_color_format,
while maintaining the DRM_COLOR_FORMAT_* compatibility to make the
transition easier.

Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260305-drm-rework-color-formats-v3-1-f3935f6db579@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>