ravb: Add support for RZ/V2M

RZ/V2M Ethernet is very similar to R-Car Gen3 Ethernet-AVB, though
some small parts are the same as R-Car Gen2.
Other differences to R-Car Gen3 and Gen2 are:
* It has separate data (DI), error (Line 1) and management (Line 2) irqs
  rather than one irq for all three.
* Instead of using the High-speed peripheral bus clock for gPTP, it has a
  separate gPTP reference clock.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>