ARM: dts: stm32: enable usb-role-switch on USB OTG on stm32mp15xx-dkx

Now that USB OTG driver supports usb role switch by overriding PHY input
signals (A-Valid, B-Valid and Vbus-Valid), enable it on stm32mp15xx-dkx.
dr_mode needn't to be forced to Peripheral anymore, it is set to OTG in
SoC device tree.
USB role (USB_ROLE_NONE, USB_ROLE_DEVICE, USB_ROLE_HOST) will be provided
by STUSB1600 Type-C controller driver.

This patch depends on "Add STUSB160x Type-C port controller support"
series, which is under review.

Signed-off-by: Amelie Delaunay <[e-mail]>
Signed-off-by: Alexandre Torgue <[e-mail]>

arch/arm/boot/dts/stm32mp15xx-dkx.dtsi

···
 };
 
 &usbotg_hs {
-	dr_mode = "peripheral";
 	phys = <&usbphyc_port1 0>;
 	phy-names = "usb2-phy";
+	usb-role-switch;
 	status = "okay";
 };