ARM: dts: sun6i: hummingbird: Add ethernet phy reset gpio properties

On the Hummingbird A31 board, the RTL8211E ethernet phy has its reset
line connect to a gpio pin, instead of floating like on other boards.
Add the stmmac properties for describing the reset gpio.

The reset delays were taken from the RTL8211E datasheet.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

arch/arm/boot/dts/sun6i-a31-hummingbird.dts

@@ -139,6 +139,9 @@ gmac: ethernet@01c30000 {
 			pinctrl-0 = <&gmac_pins_rgmii_a>;
 			phy = <&phy1>;
 			phy-mode = "rgmii";
+			snps,reset-gpio = <&pio 0 21 0>;
+			snps,reset-active-low;
+			snps,reset-delays-us = <0 10000 30000>;
 			status = "okay";
 
 			phy1: ethernet-phy@1 {