ARM: dts: omap3-igep0020-common: Introduce igep0020 common dtsi file.

Use the omap3-igep0020-common.dtsi file and remove repeated parts leaving
the nodes that are not common between IGEPv2 hardware revisions.

Signed-off-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Acked-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>