gpu: pvr: Update to DDK 1.8@795947

Change-Id: I06b43df6f86c7199b5d75dc10716e6e6b65ee9b5
gpu: pvr: Update to DDK 1.8@796887.

 - Re-introduce DC refcounting fix, which makes an unrelated (and
   unfixed) problem more reproducible.
 - Fix a bug where the driver would not wait for propagation (during
   power transitions) before performing a soft reset.

Change-Id: I88d9b6d0e434bcbcfacae967b634a0699723d35b