therm_pm72: Convert to a new-style i2c driver

The legacy i2c binding model is going away soon, so convert the
macintosh therm_pm72 driver to the new model or it will break.

This is really a quick and dirty conversion, that should do the trick
for now, but no doubt that something cleaner can be done if anyone is
interested.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Tested-by: Paul Mackerras <paulus@samba.org>