dt-bindings: iio: pressure: Add bindings for MS5637, MS5805, MS5837 and MS8607 sensors

Add device tree bindings for Measurement-Specialties MS5637, MS5805, MS5837 and MS8607 pressure & temperature sensor

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>