dt-bindings: mips: Add Serval and Jaguar2

Serval and Jaguar2 SoCs belong to the same family as Ocelot and Luton.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>