Add MMC3 support on ZOOM, which has the wl1271 device hardwired to.

The wl1271 is a 4-wire, 1.8V, embedded SDIO WLAN device with an
external IRQ line, and power-controlled by a GPIO-based fixed regulator.
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>