usb: renesas_usbhs: add a new macro for extending DnFIFOs

To extend DnFIFOs in the future, this patch adds a new macro because
some SoCs don't the "port" address for DnFIFOs.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>