drm/msm/sde: Set flush bit for slave interface

Setting flush bit for slave interface should be
skipped only for pp-split cases. For all other
cases, flush bits should be set for master and
slave interfaces when there is a change in interface
params. Add support to handle the same.

Change-Id: I8556e01f4758c39d12291ebabcd1351b2681d407
Signed-off-by: Krishna Manikandan <mkrishn@codeaurora.org>