OMAP3: update OMAP3 Beagle defconfig

Update the OMAP3 Beagle defconfig to add EHCI, MMC, TWL4030 GPIO support.
Beagle can again use MMC rootfs after this patch.  Tested on BeagleBoard
rev C2.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Jason Kridner <jkridner@beagleboard.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>