wl12xx: AP mode - encryption support

Encryption key configuration is different for AP/STA modes.

AP encryption keys are recorded when the BSS is not started. On BSS
start they are propagated to the AP (in wl1271_ap_init_hwenc).

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>