wl12xx: enable AP advanced functionality

This adjusts FW TX block allocation for connected stations in PS.
Firmware congestion is measured in allocated packets instead of blocks.

Allow a link in PS to queue up to 2 packets to the FW.

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