wlcore/wl12xx/wl18xx: implement op_set_key per HW arch

The 12xx set_key just calls the common wlcore_set_key function, in order
to program the keys into the FW.

The 18xx variant changes the spare block count when a GEM or TKIP
key is set. Also modify the get_spare_blocks HW op for 18xx to return
the correct numbers of spare blocks, according to what is currently
set in FW.

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