arm64: dts: renesas: cat875: Add rx/tx delays

The CAT875 sub board from Silicon Linux uses a Realtek PHY.

The phy driver commit bbc4d71d63 ("net: phy: realtek: fix
rtl8211e rx/tx delay config") introduced NFS mount failures.  Now it
needs both rx/tx delays for the NFS mount to work.

This patch fixes the NFS mount failure issue by adding "rgmii-id" mode
to the avb device node.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Fixes: bbc4d71d63 ("net: phy: realtek: fix rtl8211e rx/tx delay config")
Link: https://lore.kernel.org/r/20211115142830.12651-1-biju.das.jz@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

arch/arm64/boot/dts/renesas/cat875.dtsi

@@ -18,6 +18,7 @@
 	pinctrl-names = "default";
 	renesas,no-ether-link;
 	phy-handle = <&phy0>;
+	phy-mode = "rgmii-id";
 	status = "okay";
 
 	phy0: ethernet-phy@0 {