hwmon: (adt7470) Support per-sensor alarm files

Remove the old alarms hack and replace it with per-sensor alarm files.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>