arm64: dts: renesas: rzt2h-n2h-evk: Enable Ethernet support

arm64: dts: renesas: rzt2h-n2h-evk: Enable Ethernet support

Enable Ethernet support on the RZ/T2H and RZ/N2H EVKs.

Configure the MIIC converter in mode 0x6:
  Port 0 <-> ETHSW Port 0
  Port 1 <-> ETHSW Port 1
  Port 2 <-> GMAC2
  Port 3 <-> GMAC1

Enable the ETHSS, GMAC1 and GMAC2 nodes. ETHSW support will be added
once the switch driver is available.

Configure the MIIC converters to map ports according to the selected
switching mode, with converters 0 and 1 mapped to switch ports and
converters 2 and 3 mapped to GMAC ports.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20251110203926.692242-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>