Documentation: dt-bindings: update xhci-platform DT binding for R-Car H2 and M2

This commit extends the compatible string list of the xhci-platform
binding with the new "renesas,xhci-r8a7790" and "renesas,xhci-r8a7791"
compatible strings. It is used to describe the xHCI controller which
is available in the R-Car H2 and M2 SoCs.
Acked-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NYoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/usb-xhci.txt

@@ -2,7 +2,8 @@ USB xHCI controllers
 
 Required properties:
   - compatible: should be one of "generic-xhci",
-    "marvell,armada-375-xhci", "marvell,armada-380-xhci" (deprecated:
+    "marvell,armada-375-xhci", "marvell,armada-380-xhci",
+    "renesas,xhci-r8a7790", "renesas,xhci-r8a7791" (deprecated:
     "xhci-platform").
   - reg: should contain address and length of the standard XHCI
     register set for the device.