ARM: dts: sunxi: bananapi-m2-plus: Enable RGMII RX/TX delay on Ethernet PHY

The Ethernet PHY on the Bananapi M2+ has the RX and TX delays
enabled on the PHY, using pull-ups on the RXDLY and TXDLY pins.

Fix the phy-mode description to correct reflect this so that the
implementation doesn't reconfigure the delays incorrectly. This
happened with commit bbc4d71d63 ("net: phy: realtek: fix rtl8211e
rx/tx delay config").

Fixes: 8c7ba536e7 ("ARM: sun8i: bananapi-m2-plus: Enable dwmac-sun8i")
Fixes: 4904337fe3 ("ARM: dts: sunxi: Restore EMAC changes (boards)")
Fixes: aa8fee415f ("ARM: dts: sun8i: h3: Split out non-SoC-specific parts of Bananapi M2 Plus")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Jernej Skrabec <jernej.skrabec@siol.net>
Acked-by: Jernej Skrabec <jernej.skrabec@siol.net>
Link: https://lore.kernel.org/r/20201024162515.30032-8-wens@kernel.org

arch/arm/boot/dts/sunxi-bananapi-m2-plus.dtsi

@@ -126,7 +126,7 @@
 	pinctrl-0 = <&emac_rgmii_pins>;
 	phy-supply = <&reg_gmac_3v3>;
 	phy-handle = <&ext_rgmii_phy>;
-	phy-mode = "rgmii";
+	phy-mode = "rgmii-id";
 
 	status = "okay";
 };