iio: magn: bmc150: add support for bmc156

The BMC156 is a slightly less capable version of BMC150 which lacks
support for magnetometer thresholds.  Since this driver does not support
those anyway, adding support is trivial.

Datasheet is available at
https://ae-bst.resource.bosch.com/media/products/dokumente/bmc156_1/BST-BMC156-DS000-01.pdf



Signed-off-by: Vlad Dogaru <vlad.dogaru@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>