stm32mp1: migrate USBOTG device to driver model

Use the DWC2 device driver with DM_USB_GADGET support and
cleanup the USB support in STM32MP1 board.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/dts/stm32mp157c-ev1-u-boot.dtsi b/arch/arm/dts/stm32mp157c-ev1-u-boot.dtsi
index 8b92b1f..5b19e44 100644
--- a/arch/arm/dts/stm32mp157c-ev1-u-boot.dtsi
+++ b/arch/arm/dts/stm32mp157c-ev1-u-boot.dtsi
@@ -12,6 +12,7 @@
 		i2c4 = &i2c5;
 		pinctrl2 = &stmfx_pinctrl;
 		spi0 = &qspi;
+		usb0 = &usbotg_hs;
 	};
 };