wifi: ieee80211: add structs for TBTT information access

The TBTT information can have various lengths with different elements
thare are present. Add definitions for the two types that we are
interested in (i.e. the ones that contain the BSSID).

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230618214436.2a6f8766a3ec.Ic962e28492212cc8ee1eb602b8f07a4ea172fc4a@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>