R-Car AVB-DMAC has 4 Transmit start request queues, whereas
RZ/G2L has only 1 Transmit start request queue.

Add a tsrq variable to struct ravb_hw_info to handle this
difference.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>