wlcore/wl12xx: adapt FW status for multiple families

Add room for a private data struct at the end of the common FW status.
Add a convenience "counters" struct inside the FW status.

The wl12xx family does not currently use the FW status private data.

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