ARM: dts: socfpga: sodia: Fix mdio bus probe and PHY address

ARM: dts: socfpga: sodia: Fix mdio bus probe and PHY address

On SoCFPGA/Sodia board, mdio bus cannot be probed, so the PHY cannot be
found and the network device does not work.

```
stmmaceth ff702000.ethernet eth0: __stmmac_open: Cannot attach to PHY (error: -19)
```

To probe the mdio bus, add "snps,dwmac-mdio" as compatible string of the
mdio bus. Also the PHY address connected to this board is 4. Therefore,
change to 4.

Cc: stable@vger.kernel.org # 6.3+
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>