drm/msm/dp: check for VSC and VSC EXT support for HDR

Check in DPCD of the sink if VSC and VSC EXT packets are
supported. Transmission of these packets are necessary for
HDR support. If sink doesn't support these packets, do not
enable HDR.

CRs-Fixed: 2110071
Change-Id: I6f95a659faad7dadc80bac22efc4cc356a962049
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>