wl12xx: configure sleep_policy according to active roles

If there is an active AP role, stay always on.
Otherwise, allow chip to enter elp.

(Note that this is a global configuration, so if the
device is already configured according to our policy,
we don't have to configure it again)

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