dt-bindings: Add binding document for NOA1305

Document the ON Semiconductor NOA1305 ambient light sensor devicetree
bindings.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>