dt-bindings:iio:st,st-sensors: txt to yaml conversion.

This binding document covers a very large number of different sensors.
As such the existing documentation is less specific than it could
be (such as which devices have 2 interrupt pin options).
That can be improved later.

Denis, are you happy to be listed as maintainer for this one?
If not feel free to suggestion someone else.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Denis Ciocca <denis.ciocca@st.com>
Cc: Denis Ciocca <denis.ciocca@st.com>
Link: https://lore.kernel.org/r/20201031184854.745828-45-jic23@kernel.org