dt-bindings: usb: renesas,usbhs: add r8a77961 support

This patch adds support for r8a77961 (R-Car M3-W+).

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Felipe Balbi <balbi@kernel.org>