iio: accel: Add driver for the MiraMEMS DA280 3-axis 14-bit digital accelerometer

Add an iio driver for the MiraMEMS DA280 3-axis 14-bit accelerometer, as
well as for the DA226 which is a fully compatible 2-axis version.

Datasheets for the DA280 and DA226 can be found at the manufacturers site:
http://www.miramems.com/en/products.asp?list=1



Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>