usb: renesas_usbhs: add fallback compatibility strings

Add fallback compatibility strings for R-Car Gen2 and Gen3.
This is in keeping with the fallback scheme being adopted wherever
appropriate for drivers for Renesas SoCs.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

Documentation/devicetree/bindings/usb/renesas_usbhs.txt

 Renesas Electronics USBHS driver
 
 Required properties:
-  - compatible: Must contain one of the following:
+  - compatible: Must contain one or more of the following:
+
 	- "renesas,usbhs-r8a7790" for r8a7790 (R-Car H2) compatible device
 	- "renesas,usbhs-r8a7791" for r8a7791 (R-Car M2-W) compatible device
 	- "renesas,usbhs-r8a7794" for r8a7794 (R-Car E2) compatible device
 	- "renesas,usbhs-r8a7795" for r8a7795 (R-Car H3) compatible device
+	- "renesas,rcar-gen2-usbhs" for R-Car Gen2 compatible device
+	- "renesas,rcar-gen3-usbhs" for R-Car Gen3 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 register for the USBHS
   - interrupts: Interrupt specifier for the USBHS
   - clocks: A list of phandle + clock specifier pairs
@@ -22,7 +30,7 @@ Optional properties:
 
 Example:
 	usbhs: usb@e6590000 {
-		compatible = "renesas,usbhs-r8a7790";
+		compatible = "renesas,usbhs-r8a7790", "renesas,rcar-gen2-usbhs";
 		reg = <0 0xe6590000 0 0x100>;
 		interrupts = <0 107 IRQ_TYPE_LEVEL_HIGH>;
 		clocks = <&mstp7_clks R8A7790_CLK_HSUSB>;

drivers/usb/renesas_usbhs/common.c

@@ -481,6 +481,15 @@ static const struct of_device_id usbhs_of_match[] = {
 		.compatible = "renesas,usbhs-r8a7795",
 		.data = (void *)USBHS_TYPE_RCAR_GEN2,
 	},
+	{
+		.compatible = "renesas,rcar-gen2-usbhs",
+		.data = (void *)USBHS_TYPE_RCAR_GEN2,
+	},
+	{
+		/* Gen3 is compatible with Gen2 */
+		.compatible = "renesas,rcar-gen3-usbhs",
+		.data = (void *)USBHS_TYPE_RCAR_GEN2,
+	},
 	{ },
 };
 MODULE_DEVICE_TABLE(of, usbhs_of_match);