siox: add support for tracing

Implement tracing for SIOX. There are events for the data that is
written to the bus and for data being read from it.

Acked-by: Gavin Schenk <g.schenk@eckelmann.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>