dt-bindings: power: Add bindings for the Mediatek SCPSYS power domains controller

The System Control Processor System (SCPSYS) has several power management
related tasks in the system. Add the bindings to define the power
domains for the SCPSYS power controller.
Co-developed-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201030113622.201188-2-enric.balletbo@collabora.comSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>