hwmon: Add support for samples attributes

Add support for the new samples attributes to the hwmon core.

Cc: Krzysztof Adamski <krzysztof.adamski@nokia.com>
Cc: Nicolin Chen <nicoleotsuka@gmail.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>