drm/display: hdmi: Use drm_output_color_format instead of hdmi_colorspace

drm/display: hdmi: Use drm_output_color_format instead of hdmi_colorspace

The hdmi_colorspace enum was defined to represent the colorspace value
of the HDMI infoframes. It was later used by some HDMI drivers to
express the output format they should be setting up.

During the introduction of the HDMI helpers, it then was used to
represent it in the drm_connector_hdmi_state structure.

However, it's always been somewhat redundant with the DRM_COLOR_FORMAT_*
defines, and now with the drm_output_color_format enum. Let's
consolidate around drm_output_color_format in drm_connector_hdmi_state
to facilitate the current effort to provide a global output format
selection mechanism.

Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260305-drm-rework-color-formats-v3-14-f3935f6db579@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>