DOWNSTREAM: drm/msm/sde: optionally delay output fence signal

Android's HWC1 requires fences returned after a commit to be
signalled only after the next commit has been received. This
change provides a new 'output_fence_offset' property on the
CRTC to allow user space clients to optionally delay the
fence signalling by an additional commit.

Change-Id: I9938d9b746766ccdfec7568ba80eb6a7bf37b778
Signed-off-by: Clarence Ip <cip@codeaurora.org>