mx6sabresd boards can be connected to a Hannstar XGA LVDS panel.

Add support for displaying U-boot splashscreen on it.

By default, HDMI splash is selected.

In order to use splash via LVDS, do the following in the U-boot prompt:

setenv panel Hannstar-XGA
save

and reboot.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>