BACKPORT: usb: musb: Add support for MediaTek musb controller

This adds support for MediaTek musb controller in
host, peripheral and otg mode.
There are some quirk of MediaTek musb controller, such as:
 -W1C interrupt status registers
 -Private data toggle registers
 -No dedicated DMA interrupt line

Bug: 158724613
Signed-off-by: Min Guo <min.guo@mediatek.com>
Signed-off-by: Yonglong Wu <yonglong.wu@mediatek.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Link: https://lore.kernel.org/r/20200115132547.364-24-b-liu@ti.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
(cherry picked from commit 0990366bab3c6afb93b276106e1e24d4bc69db7b)
[macpaul: Resolved minor conflict in drivers/usb/musb/Kconfig and mediatek.c ]
Change-Id: I241130092bef3a7dbcc810f634004853b6f68340