ARM: OMAP3: igep0020: Set DSS pins in correct mux mode.

Platform code used to depend on bootloadres for correctly setting the mux
pin modes. But bootloaders should only set the minimum required mux pins.
So, DSS mux pins are not set in U-Boot anymore and video display is broken
on IGEPv2 when booting with newer U-Boot versions.

Setup the DSS pin muxes to enable display functionality.

Signed-off-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>