dt-bindings: mfd: rk8xx: Deprecate rockchip,system-power-controller

Deprecate support for this property in favor of standard
system-power-controller one.

Signed-off-by: Ondrej Jirman <megi@xff.cz>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20231019165732.3818789-2-megi@xff.cz


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