arm64: dts: marvell: mcbin: add support for i2c mux

The MACCHIATOBin board has a PCA9548 I2C mux for the SFP ports on
CP100 master I2C bus 1.  Add the DT description for it.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>