usb: musb-new: mt85xx: add musb-new gadget driver.

Using musb-new structure for mt85xx gadget driver.
Add gadget driver dts for mt8518 SoCs.

diff --git a/drivers/usb/musb-new/Kconfig b/drivers/usb/musb-new/Kconfig
index 79ad14e..6cf8a2b 100644
--- a/drivers/usb/musb-new/Kconfig
+++ b/drivers/usb/musb-new/Kconfig
@@ -47,6 +47,15 @@
 	bool "TI DSPS platforms"
 
 if USB_MUSB_HOST || USB_MUSB_GADGET
+config USB_MUSB_MT85XX
+	bool "Enable Mediatek MT85XX DRC USB controller"
+	depends on DM_USB && ARCH_MEDIATEK
+	default n
+	help
+	  Say y to enable Mediatek MT85XX USB DRC controller support
+	  if it is available on your Mediatek MUSB IP based platform.
+	  DMA controllers are ignored. This driver follow musb-new
+	  driver and usb gadget framework.
 
 config USB_MUSB_PIC32
 	bool "Enable Microchip PIC32 DRC USB controller"
@@ -76,7 +85,7 @@
 
 config USB_MUSB_PIO_ONLY
 	bool "Disable DMA (always use PIO)"
-	default y if USB_MUSB_AM35X || USB_MUSB_PIC32 || USB_MUSB_OMAP2PLUS || USB_MUSB_DSPS || USB_MUSB_SUNXI
+	default y if USB_MUSB_AM35X || USB_MUSB_PIC32 || USB_MUSB_OMAP2PLUS || USB_MUSB_DSPS || USB_MUSB_SUNXI || USB_MUSB_MT85XX
 	help
 	  All data is copied between memory and FIFO by the CPU.
 	  DMA controllers are ignored.