STMicroelectronics MEMS sensors

The STMicroelectronics sensor devices are pretty straight-forward I2C or
SPI devices, all sharing the same device tree descriptions no matter what
type of sensor it is.

Required properties:
- compatible: see the list of valid compatible strings below
- reg: the I2C or SPI address the device will respond to

Optional properties:
- vdd-supply: an optional regulator that needs to be on to provide VDD
  power to the sensor.
- vddio-supply: an optional regulator that needs to be on to provide the
  VDD IO power to the sensor.
- st,drdy-int-pin: the pin on the package that will be used to signal
  "data ready" (valid values: 1 or 2). This property is not configurable
  on all sensors.
- drive-open-drain: the interrupt/data ready line will be configured
  as open drain, which is useful if several sensors share the same
  interrupt line. (This binding is taken from pinctrl/pinctrl-bindings.txt)
  This is a boolean property.

Sensors may also have applicable pin control settings, those use the
standard bindings from pinctrl/pinctrl-bindings.txt.

Valid compatible strings:

Accelerometers:
- st,lis3lv02dl-accel
- st,lsm303dlh-accel
- st,lsm303dlhc-accel
- st,lis3dh-accel
- st,lsm330d-accel
- st,lsm330dl-accel
- st,lsm330dlc-accel
- st,lis331dl-accel
- st,lis331dlh-accel
- st,lsm303dl-accel
- st,lsm303dlm-accel
- st,lsm330-accel
- st,lsm303agr-accel
- st,lis2dh12-accel
- st,h3lis331dl-accel
- st,lng2dm-accel

Gyroscopes:
- st,l3g4200d-gyro
- st,lsm330d-gyro
- st,lsm330dl-gyro
- st,lsm330dlc-gyro
- st,l3gd20-gyro
- st,l3g4is-gyro
- st,lsm330-gyro
- st,lsm9ds0-gyro

Magnetometers:
- st,lsm303agr-magn
- st,lsm303dlh-magn
- st,lsm303dlhc-magn
- st,lsm303dlm-magn
- st,lis3mdl-magn

Pressure sensors:
- st,lps001wp-press
- st,lps25h-press
- st,lps331ap-press
- st,lps22hb-press
