ENGR00211133 IPUv3 fb:Check boot opt to decide if disp fb'll be present

ENGR00211133 IPUv3 fb:Check boot opt to decide if disp fb'll be present

This patch checks video boot option to decide whether we'll register
certain display framebuffer devices. The user may add video=mxcfbx:off
to kernel bootup command line to disable a display framebuffer
register. The 'x' means that the display number presented in kernel.
Defaultly, all display framebuffers will be registered if the user
doesn't specify related 'off' option in kernel bootup command line.

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