Implement two macros IEEE80211_VHTCAP_SUPP_CHAN_WIDTH_IS_160MHZ()
and its 80+80 counter part to check in vhtcaps for appropriate
levels of support and use the macros throughout the code.

Add vht160_chan_ranges/is_vht160_valid_freq and handle analogue
to vht80 in various parts of the code.

Add ieee80211_add_channel_cbw() which also takes the CBW flag
fields and make the former ieee80211_add_channel() a wrapper to it.
With the CBW flags we can add HT/VHT channels passing them to
getflags() for the 2/5ghz functions.

In ifconfig(8) add the regdomain_addchans() support for VHT160
and VHT80P80.

With this (+ regdoain.xml updates) VHT160 channels can be
configured, listed, and pass regdomain where appropriate.

Tested with:    iwlwifi
Sponsored by:   The FreeBSD Foundation
MFC after:      2 weeks
Reviewed by:    ...
Diff..:         ...