Add MMC5 support on PANDA, 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.

Based on the patch for mmc3/wl1271 device support for zoom by Ohad
Ben-Cohen <ohad@wizery.com>
Signed-off-by: Panduranga Mallireddy <panduranga_mallireddy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>