Update HDCP for external displays

So the secure flag of Display object in Display Manager (DM) can
be set correctly. HWC calls the onSync method as a workaround,
to notify SurfaceFlinger (SF) about hdcp changes, SF in turn sends
an event to DM, DM will then fetch and update display info.

Bug: 280818362
Test: manual
Change-Id: I29ce0337865b51c0fc7bf7c2d7fdd4cd6d66ef46