usb: mtu3: add tracepoints to help debug

This patch implements a few initial tracepoints for the
mtu3 driver. More traces can be added as necessary in order
to ease the task of debugging.

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