drm/msm/dp: update HDCP worker to wait for sink synchronization

Prevent HDCP worker from operating when sink synchronization has not
been achieved to prevent HDCP authentication issues with some sinks.

Change-Id: Id7948f53c60c5417306f7615c00e8a0ff7cbdeca
Signed-off-by: Christopher Braga <cbraga@codeaurora.org>
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>