drm/msm/dp: add support for HDR state machine

Add support for HDR enable/disable based on the user-space's
data. Switch to HDR pre-disable mode before disabling HDR for
smooth transition to HDR disabled state. Also, add debug
file system for HDR setup.

CRs-Fixed: 2110071
Change-Id: Iedd9f3224598eb967ec5029844c11152e350b250
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>