hwc: mdpcomp: Make all pipes available if a frame fails

Make all pipes in overlay available, if programming a frame (list)
fails. The failure could be due to commit failure, in which case the
overlay itself will make pipes available.

The failure can also be owing to lack of pipes, since we don't allow
switching pipes across mixers any more. This is particularly a problem
for split-panels. This fix addresses this latter case.

Change-Id: Ieac7ae7d03e5b9a93c7245fa160c8933593c2e09