bindings: PCI: artpec: Add support for endpoint mode

The PCIe controller integrated in ARTPEC-6 SoCs is capable of operating in
endpoint mode. Add endpoint mode support to the artpec6 driver.
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pci/axis,artpec6-pcie.txt

@@ -4,7 +4,8 @@ This PCIe host controller is based on the Synopsys DesignWare PCIe IP
 and thus inherits all the common properties defined in designware-pcie.txt.
 
 Required properties:
-- compatible: "axis,artpec6-pcie", "snps,dw-pcie"
+- compatible: "axis,artpec6-pcie", "snps,dw-pcie" for ARTPEC-6 in RC mode;
+	      "axis,artpec6-pcie-ep", "snps,dw-pcie" for ARTPEC-6 in EP mode;
 - reg: base addresses and lengths of the PCIe controller (DBI),
 	the PHY controller, and configuration address space.
 - reg-names: Must include the following entries: