omap3: overo: Use common configurations for Overo

Clean-up the board configuration file for the Gumstix Overo board by
including common omap3 definitions from ti_omap3_common.h as suggested
here [1].

[1] http://permalink.gmane.org/gmane.comp.boot-loaders.u-boot/185960



Signed-off-by: Ash Charles <ashcharles@gmail.com>

Conflicts:
	include/configs/omap3_overo.h