omap: panda: add fixed regulator device for wlan

Add a fixed regulator vmmc device to enable power control
of the wl1271 wlan device.

Based on the patch 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>