drm/msm/hdcp: Prevent disconnect from stopping HDCP

If a DP stream is disconnected when HDCP is not fully authenticated,
authentication may not continue for remaining streams. This occurs
due to the worker thread rescheduling itself on auth fail while
disconnect cancels any pending work.

Update disconnect logic to wait for HDCP authentication to complete
before stream de-registration, and reschedule the HDCP worker if HDCP
did not fully authenticate prior to disconnect.

Change-Id: I0f8934e4f34e4f5a8015587e852131795a3dad21
Signed-off-by: Christopher Braga <cbraga@codeaurora.org>