hwmon: Add driver for VIA CPU core temperature

This is a driver for the on-die digital temperature sensor of
VIA's recent CPU models.

[JD: Misc clean-ups.]

Signed-off-by: Harald Welte <HaraldWelte@viatech.com>
Cc: Juerg Haefliger <juergh@gmail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Adam Nielsen <a.nielsen@shikadi.net>