hwmon: (pmbus) Add new pmbus flag NO_WRITE_PROTECT

Some PMBus chips respond with invalid data when reading the WRITE_PROTECT
register. For such chips, this flag should be set so that the PMBus core
driver doesn't use the WRITE_PROTECT command to determine its behavior.

Signed-off-by: Erik Rosen <erik.rosen@metormote.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>