msm_fb: Allow panels to specify a second mode

This allows for panels that support more than one mode
to specify the maximum configuration. The framebuffer
size is now based on the larger of the primary and
alternate modes.  The alternate mode is also used to
check parameters when userspace is requesting a change
to the framebuffer configuration.

Change-Id: Icf644b0fb5e54fc95f45ea8c5ed97f6243cb886c
Signed-off-by: Philip Elcan <pelcan@codeaurora.org>
Signed-off-by: garwedgess <garethwilliams21@gmail.com>