ARM64: dts: marvell: cn9310: Add missing phy-mode

The DSA framework has got more picky about always having a phy-mode
for the CPU port. The SoC Ethernet is being configured to
10gbase-r. Set the switch phy-mode based on this. Additionally, the
SoC Ethernet is using in-band signalling to determine the link speed,
so add same parameter to the switch.

Additionally, the cpu label has never actually been used in the
binding, so remove it.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>