net: bcmgenet: Add BCM2711 support

The BCM2711 needs a different maximum DMA burst length. If not set
accordingly a timeout in the transmit queue happens and no package
can be sent. So use the new compatible to derive this value.

Until now the GENET HW version was used as the platform identifier.
This doesn't work with SoC-specific modifications, so introduce a proper
platform data structure.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>