ARM: dts: omap5-board-common: Use OMAP5_IOPAD pinmux macro

Use the pinmux IOPAD macros to define the register as an offset from
the padconf physical address instead of the offset from padconf base.
This 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>