hwcomposer : Fix cache redraw logic of MDP composition.

Redraw the cache if current frame cache/drop  data doesn't
match with cached frame data. Frame buffer z-order, fbcount
and mdp count are not reliable. With same fbz, fbcount and
mdpcount it is possible that layers in previous cached
frame are not part of current frame fb cache.

Change-Id: I858228dc1a3a8ab8673ab8d294e54fdbf43cc1ad
2 files changed