drm: Add DP colorspace property

This patch adds a DP colorspace property, enabling
userspace to switch to various supported colorspaces.
This will help enable BT2020 along with other colorspaces.

v2: Addressed Maarten and Ville's review comments. Enhanced
    the colorspace enum to incorporate both HDMI and DP supported
    colorspaces. Also, added a default option for colorspace.

v3: Split the changes to have separate colorspace property for
DP and HDMI.

v4: Addressed Chris and Ville's review comments, and created a
common colorspace property for DP and HDMI, filtered the list
based on the colorspaces supported by the respective protocol
standard.

v5: Merged the DP handling along with platform colorspace
handling as per Shashank's comments.

v6: Reverted to old design of exposing all colorspaces to
userspace as per Ville's review comment

v7: Fixed sparse warnings, updated the RB from Maarten and Jani's ack.

v8: Addressed Ville's review comments and updated the colorspace
macro definitions.

Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.kernel.org/patch/10809185/


Patch-mainline: dri-devel @ 02/13/2019, 12:35:09
Change-Id: I2bccd84e1793e05893d84147eb542eb434e739b3
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>