dt-binding: mfd: syscon: add Rockchip QoS register compatibles

With the conversion of syscon.yaml minItems for compatibles
was set to 2. Current Rockchip dtsi files only use "syscon" for
QoS registers. Add Rockchip QoS compatibles to reduce notifications
produced with:

make ARCH=arm dtbs_check
DT_SCHEMA_FILES=Documentation/devicetree/bindings/mfd/syscon.yaml

make ARCH=arm64 dtbs_check
DT_SCHEMA_FILES=Documentation/devicetree/bindings/mfd/syscon.yaml

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>