ath9k: recover ar9380 chips from rare stuck state

In the experiment with Azimuth ADEPT-n testbed where the APs transmit
power was reduced to 25% and the signal strength was futher attenuated
by 20dB and induced a path loss of ~7dB, the station was reporting
beacon losses and the following issue were observed.

* rx clear is stuck at low for more than 300ms
* dcu chain and complete state is stuck at one of the hang signature

This patch triggers the hang detection logic that recovers the chip
from any of the above conditions. As the issue was originally reported
in ChromeOs with AR9382 chips, this detection logic is enabled only for
AR9380/2 chips.

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