ath: introduce chirp parameter used by DFS

Some of radar types such as FCC radar type 5 require
to look up chirp in pulse to detect genuine radar and
it will prevent DFS channels from false radar detection.

Signed-off-by: Peter Oh <poh@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>