xhci: mediatek: Add support for MTK xHCI host controller

This patch is used to support the on-chip xHCI controller on
MediaTek SoCs, currently control/bulk/interrupt transfers are
supported.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Weijie Gao <weijie.gao@mediatek.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>