drm/amdgpu: display: Convert to drm_output_color_format

drm/amdgpu: display: Convert to drm_output_color_format

Now that we introduced a new drm_output_color_format enum to represent
what DRM_COLOR_FORMAT_* bits were representing, we can switch to the new
enum.

The main difference is that while DRM_COLOR_FORMAT_ was a bitmask,
drm_output_color_format is a proper enum. However, the enum was done is
such a way than DRM_COLOR_FORMAT_X = BIT(DRM_OUTPUT_COLOR_FORMAT_X) so
the transitition is easier.

The only thing we need to consider is if the original code meant to use
that value as a bitmask, in which case we do need to keep the bit shift,
or as a discriminant in which case we don't.

Acked-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Link: https://lore.kernel.org/r/20260305-drm-rework-color-formats-v3-4-f3935f6db579@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>