dt-bindings: PCI: snps,dw-pcie-ep: Add vendor specific interrupt-names

Considering that some drivers (e.g. pcie-dw-rockchip.c) already use the
interrupt-names "sys", "pmc", "msg", "err" for the device tree binding in
Root Complex mode (snps,dw-pcie.yaml), it doesn't make sense that those
drivers should use different interrupt-names when running in Endpoint mode
(snps,dw-pcie-ep.yaml).

Therefore, since "sys", "pmc", "msg", "err" are already defined in
snps,dw-pcie.yaml, add them also for snps,dw-pcie-ep.yaml.

Link: https://lore.kernel.org/linux-pci/20240607-rockchip-pcie-ep-v1-v5-2-0a042d6b0049@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/pci/snps,dw-pcie-ep.yaml

@@ -156,7 +156,7 @@ properties:
             for new bindings.
           oneOf:
             - description: See native "app" IRQ for details
-              enum: [ intr ]
+              enum: [ intr, sys, pmc, msg, err ]
 
   max-functions:
     maximum: 32