iio: Add Freescale MMA8452Q 3-axis accelerometer driver

3-axis accelerometer sensor (2/4/8 g) with 12-bit resolution
and I2C interface

many extra features are unsupported (freefall detection, orientation
change, autosleep)

datasheet is here:
http://cache.freescale.com/files/sensors/doc/data_sheet/MMA8452Q.pdf



v2: (thanks to Jonathan Cameron)
* use ARRAY_SIZE()

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>