disp: msm: dp: wait for sink to stabilize during hdcp

Some sinks need more time to stabilize after synchronization and
before it can handle an HDCP authentication request.
This change adds the delay for better interoperability.

Change-Id: I4fffb9024f782dd68e3a883208cb8e9d0c5350a1
Signed-off-by: poyewu <poyewu@codeaurora.org>