iio: temperature: max31856: Make use of device properties

Convert the module to be property provider agnostic and allow
it to be used on non-OF platforms.

Add missing mod_devicetable.h include.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220413185044.21588-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>