Document the bindings for the Sensirion SLF3S family of digital
liquid-flow sensors on I2C.  The family currently covers the
SLF3S-0600F, SLF3S-1300F and SLF3S-4000B variants.

All variants share the same register map and differ only in the flow
scale factor and the calibrated measurement range, which the driver
reads back from the product-information register.  Since that lookup
is needed in any case, a fallback compatible would buy nothing, so
each variant gets its own compatible without a fallback.  A future
drop-in compatible part can then claim one of these compatibles and
work on kernels that do not know its product ID yet.

The active calibration medium (water / IPA) is runtime-switchable
via the in_volumeflow_medium sysfs attribute and therefore not a
DT property.

Signed-off-by: Wadim Mueller <wafgo01@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>