dt-bindings: iio: st-sensors: Add LSM303C accelerometer+magnetometer

The ST LSM303C [1] is a accelerometer and magnetometer combo sensor
compatible with the existing ST sensor bindings. Accelerometer and
magnetometer are exposed through separate I2C/SPI devices, so document
separate compatibles with -accel and -magn suffix.

[1]: https://www.st.com/resource/en/datasheet/lsm303c.pdf

Signed-off-by: Stephan Gerhold <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/st,st-sensors.yaml

···
           - st,lis3lv02dl-accel
           - st,lng2dm-accel
           - st,lsm303agr-accel
+          - st,lsm303c-accel
           - st,lsm303dl-accel
           - st,lsm303dlh-accel
           - st,lsm303dlhc-accel
···
           - st,lis2mdl
           - st,lis3mdl-magn
           - st,lsm303agr-magn
+          - st,lsm303c-magn
           - st,lsm303dlh-magn
           - st,lsm303dlhc-magn
           - st,lsm303dlm-magn