usb: add MediaTek USB3 DRD driver

This patch adds support for the MediaTek USB3 DRD controller,
its host side is based on xHCI, this driver supports device mode
and host mode.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Acked-by: Bin Meng <bmeng.cn@gmail.com>