ARM: dts: omap4-panda: add DPI pinmuxing

New u-boot versions no longer set the pinmuxing for Panda's DPI output,
and the muxing has to be done in the .dts file.

Add pinmuxing for DPI and TFP410. Without these, the DVI output on Panda
does not work with recent u-boot.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>