iio: add driver for Freescale MMA9551L

iio: add driver for Freescale MMA9551L

Add support for Freescale MMA9551L Intelligent Motion-Sensing Platform.
The driver supports raw reads for acceleration and inclination, as well
as configuring inclination rate-of-change events.  The events can be
used similarly to an Android sensor Tilt event.

The specifications can be downloaded from:
http://www.freescale.com/files/sensors/doc/ref_manual/MMA955xLSWRM.pdf

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Signed-off-by: Vlad Dogaru <vlad.dogaru@intel.com>
Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>