hwmon: Add support for Lattice's POWR1220 power manager IC

This patch adds support for Lattice's POWR1220 power manager IC. Read
access to all the ADCs on the chip are supported through the hwmon
sysfs files.

Signed-off-by: Scott Kanowitz <skanowitz@echo360.com>
[Guenter Roeck: Removed some extra ( )]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>