The RZ/G3S Smarc Module has Ethernet PHYs (KSZ9131) connected to each
Ethernet IP.  For this, add proper DT descriptions to enable Ethernet
communication through these PHYs.

The interface b/w PHYs and MACs is RGMII.  The skew settings were set to
zero as based on phy-mode (rgmii-id) the KSZ9131 driver enables internal
DLL, which adds a 2ns delay b/w clocks (TX/RX) and data signals.

Different pin settings were applied to TXC and TX_CTL compared with the
rest of the RGMII pins to comply with requirements for these pins
imposed by HW manual of RZ/G3S (see chapters "Ether Ch0 Voltage Mode
Control Register (ETH0_POC)", "Ether Ch1 Voltage Mode Control Register
(ETH1_POC)", for power source selection, "Ether MII/RGMII Mode Control
Register (ETH_MODE)" for output-enable and "Input Enable Control
Register (IEN_m)" for input-enable configurations).

Also enable the Ethernet interfaces by selecting SW_CONFIG3 = SW_ON.
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20231207070700.4156557-12-claudiu.beznea.uj@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>