iio:bma180: Add BMA250 chip support

the BMA250 has only 10-bit resolution; while the data readout registers
have identical layout, the configuration is completely different compared
to the BMA180

datasheet: http://ae-bst.resource.bosch.com/media/products/dokumente/bma250/BST-BMA250-DS002-05.pdf

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Cc: Oleksandr Kravchenko <o.v.kravchenko@globallogic.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>