omap: panda: wlan board muxing

Add board muxing to support the wlan wl1271 chip that is
hardwired to mmc5 (fifth mmc controller) on the PANDA.

Based on the wlan board muxing for zoom3 by Ohad Ben-Cohen
<ohadb@ti.com>
Signed-off-by: Panduranga Mallireddy <panduranga_mallireddy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>