ARM: dts: omap3-igep0020: Use IOPAD pinmux macro

Use the OMAP3 pinmux IOPAD macro to define the physical address instead
of the offset from the padconf address. It makes the DTS easier to read
since matches the addresses listed in the Technical Reference Manual.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>