drm/bridge: lt9611: Add HPD support for lt9611

When HDMI cable was pluged in/out, it could trigger
an irq, MSM can get HPD status from LT9611, and
report the HPD status using kernel uevent to userspace.

Change-Id: I5e4a4a0d6002284d5efb29a71a3ba1d528011e6f
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>