wl12xx: add device role commands

The device role is a special role used for rx and tx frames
prior to association (as the STA role can get packets only
from its associated bssid)

Since this role is required for the sta association process,
we enable it when a new sta interface is created.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>