drm/msm: fb prepare/cleanup

Atomic wants to split the prepare/pin from where we actually program the
scanout address (so that any part that can fail is done synchronously).
Add some fb/gem apis to make this easier to use from the kms parts.

Signed-off-by: Rob Clark <robdclark@gmail.com>

diff --cc drivers/gpu/drm/msm/msm_drv.h
Simple merge

diff --cc drivers/gpu/drm/msm/msm_fb.c
Simple merge

diff --cc drivers/gpu/drm/msm/msm_gem.c
Simple merge