ARM: dts: overo: Enable McBSP2 for all Overo COMs

Both Gumstix Overo and Overo Storm COMs use TWL4030 audio module
connected to the McBSP2.  As such, enable the McBSP2 module in the
common device tree file, omap3-overo-base.dtsi, rather than in the
processor-specific device tree files, omap3-overo.dtsi and
omap3-overo-storm.dtsi.  This corrects audio on the Storm COMs where
the setting was accidentally missing from the device tree.

Signed-off-by: Ash Charles <ashcharles@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>