Add support for i2c tracepoints

This patch teaches lttng-modules about the i2c tracepoints in the Linux
kernel.

It contains the following tracepoints:

  * i2c_write
  * i2c_read
  * i2c_reply
  * i2c_result

I translated the fields and assignments from the kernel's
include/trace/events/i2c.h as well as I could.  I also tried building
this module against a kernel without CONFIG_I2C, and it built fine (the
required types are unconditionally defined).  So I don't think any "#if
CONFIG_I2C" or similar are required.

A module parameter (extract_sensitive_payload) controls the extraction
of possibly sensitive data from events.

[ With edit by Mathieu Desnoyers. ]

Signed-off-by: Simon Marchi <simon.marchi@ericsson.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>