dt-bindings: trivial-devices: Add MPS MP2971 and MP2973

Add Monolithic Power Systems MP2971 & MP2973 to trivial devices.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230714135124.2645339-2-Naresh.Solanki@9elements.com


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