arm64: dts: rockchip: add new watchdog compatible to px30.dtsi

arm64: dts: rockchip: add new watchdog compatible to px30.dtsi

The watchdog compatible strings are suppose to be SoC orientated.
In the more recently added Rockchip px30.dtsi file only
the fallback string "snps,dw-wdt" is used, so add the new
compatible string:

"rockchip,px30-wdt", "snps,dw-wdt"

make ARCH=arm64 dtbs_check
DT_SCHEMA_FILES=Documentation/devicetree/bindings/watchdog/snps,dw-wdt.yaml

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20201218120534.13788-4-jbx6244@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>