usb: renesas_usbhs: change d{0,1}fifo to dfifo array

To extend DnFIFOs in the future, this patch changes d{0,1}fifo of
usbhs_fifo_info to dfifo array.

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