arm64: dts: rockchip: add QoS register compatibles for px30

arm64: dts: rockchip: add QoS register compatibles for px30

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 for px30
to reduce notifications produced with:

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

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20201206103711.7465-4-jbx6244@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>