msm: wfd: Adds writeback start/stop functionality.

Removes register/unregister calls and replaces them
with start/stop. No need to pre-register the buffers
anymore.

Change-Id: I2f12c3a5791252ad09032cc628d93fb1dc50fee0
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>
5 files changed