rt2x00: Add support for RT3572/RT3592/RT3592+Bluetooth combo card

(based on an earlier patch submitted by Shiang)

Add support for RT3572/RT3592/RT3592+Bluetooth combo card

Signed-off-by: Shiang Tu <shiang_tu@ralinktech.com>
Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>