dt-bindings: mfd: mt8195: Add bindings for MediaTek SCPSYS

The System Control Processor System (SCPSYS) has several power
management related tasks in the system. Add the bindings for it.

Signed-off-by: Tinghan Shen <tinghan.shen@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220811025813.21492-7-tinghan.shen@mediatek.com