ath10k: limit available channels via DT ieee80211-freq-limit

Tri-band devices (1x 2.4GHz + 2x 5GHz) often incorporate special filters in
the RX and TX path. These filtered channel can in theory still be used by
the hardware but the signal strength is reduced so much that it makes no
sense.

There is already a DT property to limit the available channels but ath10k
has to manually call this functionality to limit the currrently set wiphy
channels further.

Signed-off-by: Sven Eckelmann <sven.eckelmann@openmesh.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>