drm/i915/dp: Check if force_dsc_output_format is possible

drm/i915/dp: Check if force_dsc_output_format is possible

Currently for testing an output format with DSC, we just force the
output format, without checking if it can be supported.
This also creates an issue where there is a PCON which might need to
convert from forced output format to the format to sink format.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230817142459.89764-19-ankit.k.nautiyal@intel.com