drm/msm: add support for enabling scrambling feature

To support 4k@60fps resolution through HDMI, enable
scrambler feature from HDMI controller and communicate
it with sink device through DDC.

Change-Id: I17750db358df58499303ef9d735bf3301b02a7c1
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>