drm/msm/dp: clear HDR data for each session

Clear all the data related to HDR on each DP session
tear down. This is needed to avoid using obsolete data
for next DP session.

CRs-Fixed: 2300134
Change-Id: Ifa762cf286a3323e5baa8fa1efcd79176f9f1843
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>