iio: accel: add support for the Domintech DMARD09 3-axis accelerometer

Minimal implementation of an IIO driver for the Domintech DMARD09 3-axis
accelerometer. Only supports reading the x,y,z axes at the moment.

Implementation based on the Android driver from the Acer Liquid E2
kernel sources.

Signed-off-by: Jelle van der Waa <jelle@vdwaa.nl>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>