net: dsa: sja1105: make the instantiations of struct sja1105_info constant

Since struct sja1105_private only holds a const pointer to one of these
structures based on device tree compatible string, the structures
themselves can be made const.

Also add an empty line between each structure definition, to appease
checkpatch.

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