dt-bindings:iio:temperature:melexis,mlx90632 conversion to yaml

Technically this could have gone in trivial-devices.yaml, but I have
kept it as a separate binding due to the detailed additional description
from the text file.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Crt Mori <cmo@melexis.com>
Cc: Crt Mori <cmo@melexis.com>
Link: https://lore.kernel.org/r/20201031134110.724233-26-jic23@kernel.org