hwc: Invalidate at the end of VDS pause

* On Low-end targets, no secure video is displayed on primary
during WFD session due to lack of VG pipes.

* Once the secure video is paused, and WFD session is paused
from sink, paused secure video should be seen on the primary
due to the availability of VG pipes(which are no longer used
by external)

* Call invalidate at the end of VDS pause to make this happen.

Change-Id: Ia735be10e798b6a241a82239e3a136efb54e72f3
1 file changed