drm/msm/hdcp: unload the HDCP app on DP shutdown

Unload the HDCP app whenever DP is shutdown as this ensures
that we free all resources allocated during the session.

Change-Id: I897757629cc7a7962eb5e7bd1fbc9ed0c62593cb
Signed-off-by: Sankeerth Billakanti <sbillaka@codeaurora.org>