wifi: ieee80211: split VHT definitions out
The ieee80211.h file has gotten very long, continue splitting
it by putting VHT definitions into a separate file.
Link: https://patch.msgid.link/20251105153843.c31cb771a250.I787a13064db7d80440101de3445be17881daf1b6@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>