defconfigs: enable firmware loading for AR30xx

This module is mandatory for load firmware for AR3011 on USB.

without this module :
# hcitool dev
# lsusb
Bus 001 Device 005: ID 0cf3:3005 Atheros Communications, Inc. AR3011 Bluetooth (no firmware)
[...]

with this module :
# hcitool dev
Devices:
        hci0    5C:F3:70:xx:xx:xx
# lsusb
Bus 001 Device 005: ID 0cf3:3005 Atheros Communications, Inc. AR3011 Bluetooth
[...]

Tested on U2 and U3.