iio: mma8452: add support for MMA8652FC and MMA8653FC

MMA8652FC and MMA8653FC don't provide the transient interrupt source, so
the motion interrupt source is used by providing a new iio_chan_spec
definition, so that other supported devices are not affected by this.

Datasheets for the newly supported devices are available at Freescale's
website:

http://cache.freescale.com/files/sensors/doc/data_sheet/MMA8652FC.pdf
http://cache.freescale.com/files/sensors/doc/data_sheet/MMA8653FC.pdf



Signed-off-by: Martin Kepplinger <martin.kepplinger@theobroma-systems.com>
Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>