phycore-imx8mp: add USB mass storage support

add support for USB mass storage to USB0 port of phyBOARD Pollux.

tested with "ums 0 mmc 2"

Signed-off-by: Benjamin Hahn <B.Hahn@phytec.de>
diff --git a/arch/arm/dts/imx8mp-phyboard-pollux-rdk-u-boot.dtsi b/arch/arm/dts/imx8mp-phyboard-pollux-rdk-u-boot.dtsi
index 1c7b250..b4efff2 100644
--- a/arch/arm/dts/imx8mp-phyboard-pollux-rdk-u-boot.dtsi
+++ b/arch/arm/dts/imx8mp-phyboard-pollux-rdk-u-boot.dtsi
@@ -70,6 +70,10 @@
 	bootph-pre-ram;
 };
 
+&usb_dwc3_0 {
+	dr_mode = "peripheral";
+};
+
 &usdhc2 {
 	bootph-pre-ram;
 };