dt-bindings: hwmon: add common properties

Add a common hwmon schema for two properties:
1. "label", because Linux hwmon core code parses it.
2. "shunt-resistor-micro-ohms", because several devices already use it.

Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240224-dt-bindings-hwmon-common-v2-1-b446eecf5480@linaro.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>