drm/msm: avoid wq schedule for rmfb2

rmfb2 calls wq schedule followed by flush
to buffer unreference if buffer refcount is
greater than 1. It performs the same operation
in other case also. Avoid creating workqueue
for each rmfb2 call to support simple call flow.

Change-Id: If8768469837e637221cb97a81afc822edbc6a637
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>