drm/i915: Read DSC capabilities of the HDMI2.1 PCON encoder

This patch adds support to read and store the DSC capabilities of the
HDMI2.1 PCon encoder. It also adds a new field to store these caps,
The caps are read during dfp update and can later be used to get the
PPS parameters for PCON-HDMI2.1 sink pair. Which inturn will be used
to take a call to override the existing PPS-metadata, by either
writing the entire new PPS metadata, or by writing only the
PPS override parameters.

v2: Restructured the code to read all capability DPCDs at once and store
in an array in intel_dp structure.

v3: rebase

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
[Jani: Fixed checkpatch PARENTHESIS_ALIGNMENT.]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201218103723.30844-13-ankit.k.nautiyal@intel.com