mips: dts: remove label = "cpu" from DSA dt-binding

This is not used by the DSA dt-binding, so remove it from all devicetrees.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>