ravb: Use the max frame size from hardware info for RZ/G2L

Remove the define describing the RZ/G2L maximum frame size and only use
the information in the hardware information struct. This will make it
easier to merge the R-Car and RZ/G2L code paths.

There is no functional change as both the define and the maximum frame
length in the hardware information is set to 8K.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>