hwmon: (lm78) Add individual alarm files

Add individual alarm files to the lm78 driver, these are needed by
the next version of libsensors.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>