drm/i915/display: Use sink_format instead of ycbcr420_output flag

Start passing the sink_format, to all functions that take a bool
ycbcr420_output as parameter. This will make the functions generic,
and will serve as a slight step towards 4:2:2 support later.

v2: Rebased.

v3: Correct the checks in places concerned with pipe output. (Ville)
Other minor styling and refactoring fixes, as suggested by Ville.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230427125605.487769-5-ankit.k.nautiyal@intel.com