tg3: Don't allocate jumbo ring for 5780 class devs

The 5714, 5715, and 5780 devices do not have a separate rx jumbo
producer ring.  This patch changes the code so that resources are not
allocated for it.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>