dt-bindings: mfd: Add ROHM BD71828 system-power-controller property

As the PMIC can power off the system, add the corresponding property.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/20240402111700.494004-2-andreas@kemnade.info


Signed-off-by: Lee Jones <lee@kernel.org>