dt-bindings: PCI: mediatek,mt7621-pcie: Switch from deprecated pci-bus.yaml

dtschema package with core schemas deprecated pci-bus.yaml schema in
favor of individual schemas per host, device and pci-pci.

Switch Mediatek MT7621 PCIe host bridge binding to this new schema.

This requires dtschema package newer than v2024.02 to work fully.
v2024.02 will partially work: with a warning.

Link: https://lore.kernel.org/linux-pci/20240413151617.35630-4-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>

Author: krzk

Documentation/devicetree/bindings/pci/mediatek,mt7621-pcie.yaml

@@ -14,7 +14,7 @@ description: |+
   with 3 Root Ports. Each Root Port supports a Gen1 1-lane Link
 
 allOf:
-  - $ref: /schemas/pci/pci-bus.yaml#
+  - $ref: /schemas/pci/pci-host-bridge.yaml#
 
 properties:
   compatible:
@@ -33,7 +33,7 @@ properties:
 patternProperties:
   '^pcie@[0-2],0$':
     type: object
-    $ref: /schemas/pci/pci-bus.yaml#
+    $ref: /schemas/pci/pci-pci-bridge.yaml#
 
     properties:
       reg: