ARM: dts: omap3-igep0020: Add pinmuxing for DVI output

The IGEPv2 has a TFP410 DPI-to-DVI encoder attached to OMAP's
Display SubSystem (DSS).

Add mux setup for DSS pins and also for the GPIO 170 pin that
is used to ensure that the DVI-D is powered down on power up.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>