hwmon (occ): Add sensor types and versions

Add structures to define all sensor types and versions. Add sysfs show
and store functions for each sensor type. Add a method to construct the
"set user power cap" command and send it to the OCC. Add rate limit to
polling the OCC (in case user-space reads our hwmon entries rapidly).

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>