[PATCH RTEMS v2] Add i2c command

[chrisj at rtems.org]

The patch adds an i2c command. It is a single command to test and 
explore I2C buses on hardware. The command lets you string together
reads and writes on a single command line to access a number of devices
so you can script basic functionality simply.

This command adds to the existing i2cdetect, i2cset and i2cget. I have
left those command as they are and we can decide on their future once
this patch is merged.

v2:
- Switch the detect to a zero length write. Add `-rw` option to detect
  as a fallback option to use reads and then writes.

Chris