mac80211: ath9k-htc: support "chanbw" in debugfs

mac80211: ath9k-htc: support "chanbw" in debugfs

ath9k-htc USB-based adapters also support 5/10MHz channel bandwidth.
Move the code handling the features in debugfs to common-debug.c,
and create proper registration functions to use in debug.c and
htc_drv_debug.c, leaving only debugfs registration there.

While at that, refresh one patch that would conflict otherwise.

Tested on TP-Link Archer C7v2 (ath79) and TP-Link WN722Nv1 (AR9287)
and WN822Nv2 (AR7010+AR9287).

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>