disp: msm: dp: populate supported colorspace property for DP

Populate the supported colorspaces property for DP
as part of getting the display modes.

This will expose the supported colorspaces of the sink to
userspace and in-turn the userspace shall pick the colorspace
suitable for the use-case.

Change-Id: I70408c719610bc63f9c06dad8cd50f7fa5d94908
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>