ARM: mxs: use auxdata to attach mxsfb_platform_data

Use auxdata to attach mxsfb_platform_data for imx23-evk and imx28-evk.
We take this as a temporary solution for removing those board files,
and it should be updated to use common bindings for struct fb_videomode
when it becomes available.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>