drm/msm: enable hpd event support for hdmi display

When HPD is enabled in DTSI for HDMI display, driver needs to poll
the HPD status change and report event back to user space.

Change-Id: I6dd2f3078875698ff8cfd7bdb7cfd662e85eec9b
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>