net: dsa: sja1105: expose static config as devlink region

As explained in Documentation/networking/dsa/sja1105.rst, this switch
has a static config held in the driver's memory and re-uploaded from
time to time into the device (after any major change).

The format of this static config is in fact described in UM10944.pdf and
it contains all the switch's settings (it also contains device ID, table
CRCs, etc, just like in the manual). So it is a useful and universal
devlink region to expose to user space, for debugging purposes.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>