drm/msm/hdcp: Extend SDE HDCP to support stream registration

MST HDCP functionality requires lower level HDCP libraries to
be aware of all active DP MST streams. Update the HDCP interface
to support DP MST mode, and allow drivers to register and deregister
streams for use with HDCP.

Change-Id: I03b89a8f34056c7f92c7483d0503f47b007b6f6b
Signed-off-by: Christopher Braga <cbraga@codeaurora.org>
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>