ravb: Add aligned_tx to struct ravb_hw_info

R-Car Gen2 needs a 4byte aligned address for the transmission buffer,
whereas R-Car Gen3 doesn't have any such restriction.

Add aligned_tx to struct ravb_hw_info to select the driver to choose
between aligned and unaligned tx buffers.

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>