msm: mdss: hdmi: add sysfs node for audio video latency

Add edid_audio_latency and edid_video_latency sysfs nodes to
report the info extracted from edid. AV sync can use these info
to compensate the difference.

Change-Id: I2b1a3f6c0e2d892be8d41651ea898ce47c9d820b
Signed-off-by: Ken Zhang <kenz@codeaurora.org>