ARM: dts: omap3-overo: Enable WiFi/BT combo

MMC2 is used by the on-board WiFi module populated on some boards
(based on Marvell Libertas 8688 SDIO). The Bluetooth is connected
to UART2.

Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Signed-off-by: Tony Lindgren <tony@atomide.com>