Add support for the AR9285 chipset, which is found on many netbooks

Add support for the AR9285 chipset, which is found on many netbooks
available today.

This card is a low power 802.11bgn that only does 11n rates up to MCS 7
(that's 65 Mbps in 20Mhz mode and 135 in 40Mhz mode).
802.11n is  not yet supported, but will be in the future.

The driver still has a problem regarding to the setting of txpower on
the card, so don't expect good performance yet. After fixing this
problem, an MFC is possible.

Special thanks to iXsystems and S Smirnov <tonve at yandex.ru> for help
with the purchase of a netbook with this card.

Sponsored by:	iXsystems, Inc.