ath9k_hw: Improve fast channel change for AR9003 chips

In order to reduce the overall scan time, fast channel change
should be implemented properly. This patch adds fast channel
change support across band switch or channel mode switch
instead of doing full chip reset. During the fastcc, tx iqcal
measurements are preserved and will be reloaded after successful
the channel change.

This patch also addressed fast channel issue where the STA can not
see APs in higher than operating channel on 5GHz band after
the association.

Cc: Paul Stewart <pstew@google.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>