dt-bindings: power: Add starfive,jh7110-pmu

Add bindings for the Power Management Unit on the StarFive JH7110 SoC.

Signed-off-by: Walker Chen <walker.chen@starfivetech.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>