iio: accel: Add support for Bosch BMA220

This commit adds basic support for the Bosch Sensortec BMA220
digital triaxial acceleration sensor.
The device datasheet can be found here:

http://www.mouser.com/pdfdocs/BSTBMA220DS00308.PDF



Includes:
- raw readings
- ACPI detection
- power management

Signed-off-by: Tiberiu Breana <tiberiu.a.breana@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>