usb: mtu3: mtu3_trace: Supply missing mtu3_debug.h include file

If the header file containing a function's prototype isn't included by
the sourcefile containing the associated function, the build system
complains of missing prototypes.

Fixes the following W=1 kernel build warning(s):

drivers/usb/mtu3/mtu3_trace.c:13:6: warning: no previous prototype for ‘mtu3_dbg_trace’ [-Wmissing-prototypes]
13 | void mtu3_dbg_trace(struct device *dev, const char *fmt, ...)
| ^~~~~~~~~~~~~~

Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mediatek@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200715093209.3165641-5-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: mtu3: mtu3_trace: Function headers are not suitable for kerneldoc

Kerneldoc headers should only be used to document functions and data
structures.

Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc: linux-mediatek@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200715093209.3165641-4-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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>