arm: mvebu: helios4: Reset uSOM onboard phy during board init

Similar to Clearfog rev 2.1, GPIO 19 also used to reset onboard ethernet
PHY.

This patch depend on
net: mvneta: Add GPIO configuration support
[URL: https://patchwork.ozlabs.org/patch/1007736/]
Signed-off-by: NAditya Prayoga <aditya@kobol.io>
Reviewed-by: NStefan Roese <sr@denx.de>
Tested-By: NDennis Gilmore <dgilmore@redhat.com>
Reviewed-By: NDennis Gilmore <dgilmore@redhat.com>
Signed-off-by: NStefan Roese <sr@denx.de>

arch/arm/dts/armada-388-helios4-u-boot.dtsi

@@ -8,6 +8,10 @@
 	};
 };
 
+&eth0 {
+	phy-reset-gpios = <&gpio0 19 GPIO_ACTIVE_LOW>;
+};
+
 &spi1 {
 	u-boot,dm-spl;
 };