arm64: dts: imx8mn-evk: add two parameters for samsung picophy tuning

With these two parameters tuning, it can pass USB eye diagram at evk board.
Signed-off-by: NPeter Chen <peter.chen@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mn-evk.dtsi

@@ -132,6 +132,8 @@
 	srp-disable;
 	adp-disable;
 	usb-role-switch;
+	samsung,picophy-pre-emp-curr-control = <3>;
+	samsung,picophy-dc-vol-level-adjust = <7>;
 	status = "okay";
 
 	port {