iio:magnetometer: Add STMicroelectronics magnetometers driver

This patch adds a generic magnetometer driver for STMicroelectronics
magnetometers, currently it supports:
LSM303DLHC, LSM303DLM, LIS3MDL.

Signed-off-by: Denis Ciocca <denis.ciocca@st.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
7 files changed