wlcore/wl12xx: create per-chip-family private storage

This storage is allocated in wlcore_alloc_hw and freed in free_hw. The
size of the storage is determined by the low-level driver.

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