Fourth set of IIO new device support, features and cleaups for the 4.10 cycle.
Probably the final set before the merge window unless things get significantly
delayed.
New device support
* STM32 ADC core
- new driver. Interesting device with up to 3 ADCs with complex triggering
options that will follow later. Note split into an 'mfd like' core that
handles the interrupt sharing etc between the various instances present and
a per ADC section that is instantiated as many times as needed.
- device tree bindings.
Cleanups and minor fixes
* st_accel
- inline per sensor data as the defines don't add any meaning and make it
much harder to check if a given sensor has the right values.
* hid-magnetometer
- sort out the associations of the associated attributes with the two types.