dt-bindings: arm: samsung: pmu: Add missing properties

Add common properties appearing in DTSes (assigned-clock-parents,
assigned-clocks) to fix dtbs_check warnings like:

  arch/arm64/boot/dts/exynos/exynos5433-tm2.dt.yaml: system-controller@105c0000:
    'assigned-clock-parents', 'assigned-clocks' do not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200903191311.12293-1-krzk@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/samsung/pmu.yaml

@@ -45,6 +45,9 @@ properties:
   reg:
     maxItems: 1
 
+  assigned-clock-parents: true
+  assigned-clocks: true
+
   '#clock-cells':
     const: 1