ARM: S3C: Update hwmon device definition and name

Change the hwmon device name to something more generic as this
should be functional for both the s3c24xx and s3c64xx archs.

Since it has yet to have a driver, it is pretty safe to change
as there are no extant users.

Also add the necessary entry in devs.h which seems to have been
missed  out at somepoint.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>