ath10k: add spectral scan feature

Adds the spectral scan feature for ath10k. The spectral scan is triggered by
configuring a mode through a debugfs control file. Samples can be gathered via
another relay debugfs file.

Essentially, to try it out:

ip link set dev wlan0 up
echo background > /sys/kernel/debug/ieee80211/phy0/ath10k/spectral_scan_ctl
echo trigger > /sys/kernel/debug/ieee80211/phy0/ath10k/spectral_scan_ctl
iw dev wlan0 scan
echo disable > /sys/kernel/debug/ieee80211/phy0/ath10k/spectral_scan_ctl
cat /sys/kernel/debug/ieee80211/phy0/ath10k/spectral_scan0 > samples

This feature is still experimental. Based on the original RFC patch of
Sven Eckelmann.

Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath10k/mac.c

@@ -2499,6 +2499,8 @@ static int ath10k_start(struct ieee80211_hw *hw)
 	ar->num_started_vdevs = 0;
 	ath10k_regd_update(ar);
 
+	ath10k_spectral_start(ar);
+
 	mutex_unlock(&ar->conf_mutex);
 	return 0;
 
@@ -2909,8 +2911,14 @@ static void ath10k_remove_interface(struct ieee80211_hw *hw,
 		dev_kfree_skb_any(arvif->beacon);
 		arvif->beacon = NULL;
 	}
+
 	spin_unlock_bh(&ar->data_lock);
 
+	ret = ath10k_spectral_vif_stop(arvif);
+	if (ret)
+		ath10k_warn("failed to stop spectral for vdev %i: %d\n",
+			    arvif->vdev_id, ret);
+
 	ar->free_vdev_map |= 1 << (arvif->vdev_id);
 	list_del(&arvif->list);