wifi: ieee80211: split HE definitions out

The ieee80211.h file has gotten very long, continue splitting
it by putting HE definitions into a separate file.

Link: https://patch.msgid.link/20251105153843.6998c0802104.I3dd7cfea6abbd118b999ecdedd48437d39cb0533@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>