dt-bindings: PCI: mediatek-gen3: Add mediatek,pbus-csr phandle array property

Introduce the mediatek,pbus-csr property for the pbus-csr syscon node
available on EN7581 SoC.

The Airoha pbus-csr block provides a configuration interface for the
PBUS controller used to detect if a given address is accessible on PCIe
controller.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20250225-en7581-pcie-pbus-csr-v4-1-24324382424a@kernel.org
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml

@@ -109,6 +109,17 @@ properties:
   power-domains:
     maxItems: 1
 
+  mediatek,pbus-csr:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    items:
+      - items:
+          - description: phandle to pbus-csr syscon
+          - description: offset of pbus-csr base address register
+          - description: offset of pbus-csr base address mask register
+    description:
+      Phandle with two arguments to the syscon node used to detect if
+      a given address is accessible on PCIe controller.
+
   '#interrupt-cells':
     const: 1
 
@@ -168,6 +179,8 @@ allOf:
           minItems: 1
           maxItems: 2
 
+        mediatek,pbus-csr: false
+
   - if:
       properties:
         compatible:
@@ -197,6 +210,8 @@ allOf:
           minItems: 1
           maxItems: 2
 
+        mediatek,pbus-csr: false
+
   - if:
       properties:
         compatible:
@@ -224,6 +239,8 @@ allOf:
           minItems: 1
           maxItems: 2
 
+        mediatek,pbus-csr: false
+
   - if:
       properties:
         compatible: