iio: common: ssp_sensors: Add sensorhub accelerometer sensor

This patch adds accelerometer iio driver which uses sensorhub as data
provider.

Signed-off-by: Karol Wrona <k.wrona@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>