ARM: OMAP: enable TWL4030_USB in omap2plus_defconfig

Enable TWL4030_USB which is used at least on Nokia N900/N950/N9 (OMAP3)
and BeagleBoard.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>