msm: mdss: Relocate timing flush for avr vtotal setup

The AVR vtotal setup is done during ctl start. Since the slave
ctl is not yet setup, currently the master and slave controls
get flushed independently even though it is a split display
setup. Instead, just set a flag and then do the actual flush
as part of commit when the controls are properly setup.

Change-Id: I8eb1693c9a3a6404d28a82cab9a9f0ce58d1bb03
Signed-off-by: Rajkumar Subbiah <rsubbia@codeaurora.org>