dt-bindings: PCI: mediatek: Add Airoha EN7532 support

Add a binding for Airoha EN7532, an ARM-based platform SoC integrating the
same PCIe IP as MT7622.

Link: https://lore.kernel.org/r/20220615125335.96089-1-nbd@nbd.name
Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>

Author: blogic

Documentation/devicetree/bindings/pci/mediatek-pcie.txt

@@ -7,6 +7,7 @@ Required properties:
 	"mediatek,mt7622-pcie"
 	"mediatek,mt7623-pcie"
 	"mediatek,mt7629-pcie"
+	"airoha,en7523-pcie"
 - device_type: Must be "pci"
 - reg: Base addresses and lengths of the root ports.
 - reg-names: Names of the above areas to use during resource lookup.