docs: networkng: convert sja1105's devlink info to RTS

A new file snuck into the tree after all existing documentation
was converted to RST. Convert sja1105's devlink info and move
it where the rest of the drivers are documented.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>