Add meas-spec sensors common part

Measurement specialties drivers common part.
These functions are used by further drivers
in the patchset: TSYS01, TSYS02D, HTU21, MS5637, MS8607

Signed-off-by: Ludovic Tancerel <ludovic.tancerel@maplehightech.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>