drm/msm/sde: reduce bandwidth at commit done

Reductions in requested bandwidth can be done after the
current commit is accepted by hardware. It isn't necessary
to wait until the current frame is completed. Move the
reduced bandwidth vote from the frame done event thread
to the commit thread, after the new frame has been
accepted. This avoids a race condition between the frame
done for the previous thread and the frame flush for
the current thread.

Change-Id: I6499438a3c6eba3b26656708955fb723704f492b
Signed-off-by: Clarence Ip <cip@codeaurora.org>