fixes for [2474091] Saw Poor behaviour playing a video.

- fix a bug when hacking video buffers into gralloc buffers
 where the buffer size was incorrect this was causing the
 "direct-form-texture" mode to fail

- also when the above fails, make sure to revert to the
 "mdp copy mode" before going to "slow mode"

- finally disable completely the "direct-from-texture" mode
 for now. It cannot work because the allocated buffers can't
 respect the GPU constraints (alignment and such). We'll
 have to find a solution for that.