arm64: dts: ti: k3-am642-evm: add overlay for ICSSG1 2nd port

The am642-evm doesn't allow to enable 2 x CPSW3g ports and 2 x ICSSG1 ports
all together, so base k3-am642-evm.dts enables by default 2 x CPSW3g ports
and 1 x ICSSG1 ports, but it is also possible to support 1 x CPSW3g ports
and 2 x ICSSG1 ports configuration.

This patch adds overlay to support 1 x CPSW3g ports and 2 x ICSSG1 ports
configuration:
- Add label name 'mdio_mux_1' for 'mdio-mux-1' node so that the node
'mdio-mux-1' can be disabled in the overlay using the label name.
- disable 2nd CPSW3g port
- update CPSW3g pinmuxes to not use RGMII2
- disable mdio-mux-1 and define mdio-mux-2 to route ICSSG1 MDIO to the
shared DP83869 PHY
- add and enable ICSSG1 RGMII2 pinmuxes
- enable ICSSG1 MII1 port

Reviewed-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Link: https://lore.kernel.org/r/20240215103036.2825096-4-danishanwar@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>