drm/amd/display: cache additional dpcd caps for HDR capability check

[Why]
Currently we are missing a few checks to see if HDR10 is allowed.
In particular we never check for the extended colorimetry bit (whether its
present or set to 1). Further we don't read in the dpcd block in DC that
would provide these bits.

[How]
- Added in DC code to read in the block containing the extended colorimetry
bit.

Signed-off-by: Harmanprit Tatla <Harmanprit.Tatla@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>