dt-bindings: soc: add header files required for MT7623A SCPSYS dt-binding

Add relevant header files required for dt-bindings of SCPSYS power domain
control for subsystems found on MT7623A SoC.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Cc: Rob Herring <robh@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
[mb: clean-up commit message]
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>