msm_fb: Avoid multiple disable calls for vsync interrupt

For LCDC and DSI Video mode panels, there seem to be multiple
disable calls for Vsync interrupt term. Change to avoid this
issue by proper synchronization of vsync term and DMA term.

Change-Id: Iaf11ba92cc7db55c6196add2d7dea581cb29fc8a
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>