wlcore: create private static_data area and add operation to parse it

The wl18xx firmware has more information in the static_data than
wl12xx.  To be able to parse that in an abstracted way, this patch
adds a priv area to the static data struct and an operation that
allows the lower driver to parse it if necessary.

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