The DP standard leaves ambiguity to if sink synchronization
will be set before auxiliary protocols such as HDCP are to begin.
Update the dp_display HDCP worker to check sink sync only if
explicitly instructed to via the new debugfs node 'hdcp_wait_sink_sync'
Change-Id: I4f4d0b14096aa3dc498e47de557de14092d37a58
Signed-off-by: Christopher Braga <cbraga@codeaurora.org>