usb: renesas_usbhs: add SoC names to compatibility string documentation

This extends the documentation of compatibility strings a little to
include the SoC names.
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

@@ -2,10 +2,10 @@ Renesas Electronics USBHS driver
 
 Required properties:
   - compatible: Must contain one of the following:
-	- "renesas,usbhs-r8a7790"
-	- "renesas,usbhs-r8a7791"
-	- "renesas,usbhs-r8a7794"
-	- "renesas,usbhs-r8a7795"
+	- "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
   - 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