omap: pandora: fix wifi support

After commit ed919b01 "mmc: sdio: fix runtime PM anomalies by introducing
MMC_CAP_POWER_OFF_CARD" it is required to specify MMC_CAP_POWER_OFF_CARD
to have runtime PM support. As the wl1251 driver expects card to be
powered down when it's not used, wifi will no longer work after interface
is brought down at least once without functioning runtime PM.

Fix this by declaring MMC_CAP_POWER_OFF_CARD for MMC3.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>