wl12xx: AP mode - add STA add/remove ops

Allocate and free host link IDs (HLIDs) for each link. A per-STA
data structure keeps the HLID of each STA.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>