usb: mtu3: host only mode support

supports host only mode and the code is ported from
host/xhci-mtk.c
IPPC register shared between host and device is moved
into common glue layer.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>