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/Makefile b/drivers/usb/musb-new/Makefile
index ec7852c..6355eb1 100644
--- a/drivers/usb/musb-new/Makefile
+++ b/drivers/usb/musb-new/Makefile
@@ -8,6 +8,7 @@
 obj-$(CONFIG_USB_MUSB_DSPS) += musb_dsps.o
 obj-$(CONFIG_USB_MUSB_DA8XX)	+= da8xx.o
 obj-$(CONFIG_USB_MUSB_AM35X) += am35x.o
+obj-$(CONFIG_USB_MUSB_MT85XX) += mt85xx.o
 obj-$(CONFIG_USB_MUSB_OMAP2PLUS) += omap2430.o
 obj-$(CONFIG_USB_MUSB_PIC32) += pic32.o
 obj-$(CONFIG_USB_MUSB_SUNXI) += sunxi.o