dt-bindings: hwmon: Allow specifying channels for lm90

Add binding description for temperature channels. Currently, support for
label and temperature-offset-millicelsius is implemented.

Signed-off-by: Slawomir Stepien <slawomir.stepien@nokia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220525073657.573327-3-sst@poczta.fm


Signed-off-by: Guenter Roeck <linux@roeck-us.net>