PCI: rcar: Add gen2 fallback compatibility string for pcie-rcar

Add fallback compatibility string for R-Car Gen 2 family.  This is in
keeping with the fallback scheme being adopted wherever appropriate for
drivers for Renesas SoCs.
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

Documentation/devicetree/bindings/pci/rcar-pci.txt

 * Renesas RCar PCIe interface
 
 Required properties:
-- compatible: should contain one of the following
-	"renesas,pcie-r8a7779", "renesas,pcie-r8a7790", "renesas,pcie-r8a7791",
-	"renesas,pcie-r8a7795"
+compatible: "renesas,pcie-r8a7779" for the R8A7779 SoC;
+	    "renesas,pcie-r8a7790" for the R8A7790 SoC;
+	    "renesas,pcie-r8a7791" for the R8A7791 SoC;
+	    "renesas,pcie-r8a7795" for the R8A7795 SoC;
+	    "renesas,pcie-rcar-gen2" for a generic R-Car Gen2 compatible device.
+
+	    When compatible with the generic version, nodes must list the
+	    SoC-specific version corresponding to the platform first
+	    followed by the generic version.
+
 - reg: base address and length of the pcie controller registers.
 - #address-cells: set to <3>
 - #size-cells: set to <2>
@@ -26,7 +33,7 @@ Example:
 SoC specific DT Entry:
 
 	pcie: pcie@fe000000 {
-		compatible = "renesas,pcie-r8a7791";
+		compatible = "renesas,pcie-r8a7791", "renesas,pcie-rcar-gen2";
 		reg = <0 0xfe000000 0 0x80000>;
 		#address-cells = <3>;
 		#size-cells = <2>;

drivers/pci/host/pcie-rcar.c

@@ -915,6 +915,7 @@ static int rcar_pcie_parse_map_dma_ranges(struct rcar_pcie *pcie,
 
 static const struct of_device_id rcar_pcie_of_match[] = {
 	{ .compatible = "renesas,pcie-r8a7779", .data = rcar_pcie_hw_init_h1 },
+	{ .compatible = "renesas,pcie-rcar-gen2", .data = rcar_pcie_hw_init },
 	{ .compatible = "renesas,pcie-r8a7790", .data = rcar_pcie_hw_init },
 	{ .compatible = "renesas,pcie-r8a7791", .data = rcar_pcie_hw_init },
 	{ .compatible = "renesas,pcie-r8a7795", .data = rcar_pcie_hw_init },