dt-bindings: iio: accel: Add SCA3300 documentation

initial DT bindings for Murata SCA3300 Accelerometer.

Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210426081041.59807-2-tomas.melin@vaisala.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>