ath9k: add support for DFS master mode

These are the remaining knobs in ath9k to support DFS:
* mark AR9280 and AR9580 as DFS tested
* synchronize DFS regulatory domain to reg notifyer
* set required RX filter flags for radar detection
* process radar PHY errors at DFS detector
* notify DFS master on radar detection

DFS support requires CONFIG_ATH9K_DFS_CERTIFIED to be set.

Signed-off-by: Zefir Kurtisi <zefir.kurtisi@neratec.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>