arm: dts: imx8mp-evk: Add FEC PHY reset timing

Add phy-reset-duration and phy-reset-post-delay to FEC node for PHY
reset, otherwise the PHY does not work correctly.

Signed-off-by: Ye Li <ye.li@nxp.com>
diff --git a/arch/arm/dts/imx8mp-evk-u-boot.dtsi b/arch/arm/dts/imx8mp-evk-u-boot.dtsi
index 0bf6ef5..6a91404 100644
--- a/arch/arm/dts/imx8mp-evk-u-boot.dtsi
+++ b/arch/arm/dts/imx8mp-evk-u-boot.dtsi
@@ -142,4 +142,6 @@
 
 &fec {
 	phy-reset-gpios = <&gpio4 2 GPIO_ACTIVE_LOW>;
+	phy-reset-duration = <15>;
+	phy-reset-post-delay = <100>;
 };