ravb: Add multi_irq to struct ravb_hw_info

R-Car Gen3 supports separate interrupts for E-MAC and DMA queues,
whereas R-Car Gen2 and RZ/G2L have a single interrupt instead.

Add a multi_irq hw feature bit to struct ravb_hw_info to enable
this only for R-Car Gen3.

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>