dt-bindings: PCI: cdns,cdns-pcie-host: Drop redundant msi-parent and pci-bus.yaml

The binding reference common cdns-pcie-host.yaml, which already defines
msi-parent and has a reference to pci-bus.yaml schema. Drop redundant
pieces here to make it a bit smaller.

Link: https://lore.kernel.org/linux-pci/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Krzysztof Wilczyński <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Acked-by: Sergio Paracuellos <[e-mail]>

Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml

···
   - Tom Joseph <[e-mail]>
 
 allOf:
-  - $ref: /schemas/pci/pci-bus.yaml#
   - $ref: cdns-pcie-host.yaml#
 
 properties:
···
     items:
       - const: reg
       - const: cfg
-
-  msi-parent: true
 
 required:
   - reg