hwmon: (w83781d) Add individual alarm and beep files

The upcoming libsensors 3 needs these individual alarm and beep files.
For the W83781D, this is quirky because this chip has a single alarm
bit for both temp2 and temp3.

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>