drm/msm: add checksum for HDR infoframe

Checksum for the HDR infoframe is set to zero by default
as this is not a mandatory field as per the HDMI spec.

However certain HDMI sinks still expect a non-zero
checksum. Otherwise they disregard the infoframe
and the sink does not enter HDR mode despite other fields
of the infoframe being valid.

Add a valid checksum to the HDR infoframe to improve
interoperability of our HDR solution for HDMI.

Change-Id: Ie826e5e637fc1f053203bdcf6a829d0246a9ed67
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>