ath9k: Add a HW flag for FCC

Fast Channel Change across 2G/5G bands is supported
only by AR9462 and AR9565. Add a HW capability field
to indicate this.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>