drm/msm: disable HDCP before turning off timing engine

As per the hardware programming sequence, HDCP authentication
process must start after turning ON the timing engine and the
authentication process should be stopped before turning OFF
the timing engine.

Implement this sequence during the HDMI turn OFF sequence.

Also, make sure to wait for one frame before disabling the DDC
while turning OFF the HDCP. This is required to make sure we
receive the HDCP encryption disabled interrupt before disabling
the HW.

Change-Id: I3174f51fe1b6ab578db2d38caaf761444e6ebd8f
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>