ENGR00279204-1 mxc vout: reconfig fb when necessary

ENGR00279204-1 mxc vout: reconfig fb when necessary

Users may call VIDIOC_S_CTRL or VIDIOC_S_CROP ioctrls
to update streaming parameters on-the-fly after video
has been streamed on, such as for rotation/output
resolution/overlay output position change. Any
unnecessary frame buffer reconfiguration would cause
a pair of frame buffer blank/unblank events happen and
even makes the background framebuffer show up for a
short period of time if the video is rendered on an
overlay framebuffer. This patch compares the last time
video output pipe line settings with the current ones
to determine whether frame buffer reconfiguration is
necessary or not.

Signed-off-by: Liu Ying <Ying.Liu@freescale.com>