board: Enable ethernet, tftpboot support to pic32mzdask board.

This adds ethernet, TFTP support for PIC32MZ[DA] Starter Kit. Also
custom environment variables/scripts are added to help boot from network.

Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
diff --git a/arch/mips/dts/pic32mzda_sk.dts b/arch/mips/dts/pic32mzda_sk.dts
index f886a0f..e5ce0bd 100644
--- a/arch/mips/dts/pic32mzda_sk.dts
+++ b/arch/mips/dts/pic32mzda_sk.dts
@@ -42,4 +42,14 @@
 
 &sdhci {
 	status = "okay";
+};
+
+&ethernet {
+	reset-gpios = <&gpioJ 15 0>;
+	status = "okay";
+	phy-mode = "rmii";
+	phy-handle = <&ethernet_phy>;
+	ethernet_phy: lan8740_phy@0 {
+		reg = <0>;
+	};
 };
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