usb: dwc3: Add phy interface for dwc3_uboot

U-Boot has two different variants of dwc3 initializations,
- with dm variant gadget, so the respective dm driver would
  call the dwc3_init in core.
- with non-dm variant gadget, so the usage board file would
  call dwc3_uboot_init in core.

The driver probe would handle all respective gadget properties
including phy interface via phy_type property and then trigger
dwc3_init for dm-variant gadgets.

So, to support the phy interface for non-dm variant gadgets,
the better option is dwc3_uboot_init since there is no
dedicated controller for non-dm variant gadgets.

This patch support for adding phy interface like 8/16-bit UTMI+
code for dwc3_uboot.

This change used Linux phy.h enum list, to make proper code
compatibility.

Cc: Marek Vasut <marex@denx.de>
Tested-by: Levin Du <djw@t-chip.com.cn>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>

include/linux/usb/phy.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * USB PHY defines
+ *
+ * These APIs may be used between USB controllers.  USB device drivers
+ * (for either host or peripheral roles) don't use these calls; they
+ * continue to use just usb_device and usb_gadget.
+ */
+
+#ifndef __LINUX_USB_PHY_H
+#define __LINUX_USB_PHY_H
+
+enum usb_phy_interface {
+	USBPHY_INTERFACE_MODE_UNKNOWN,
+	USBPHY_INTERFACE_MODE_UTMI,
+	USBPHY_INTERFACE_MODE_UTMIW,
+};
+
+#endif /* __LINUX_USB_PHY_H */