None of mxsfb users uses mxsfb_platform_data now.  Let's remove it
from mxsfb driver.

As the result, include/linux/mxsfb.h gets deleted with a few macros
moved into mxsfb.c.  Along with the change, the typo "FAILING" in macro
name is fixed to be "FALLING".
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>