wlcore: abstract debugfs fw_stats to be handled by the lower drivers

The FW statistics differ from hardware to hardware.  This commit
prepares for hardware-specific implementation of the FW statistics
debugfs entries.

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