bnx2x: Fixed ethtool -d for 578xx

Registers dump code erroneously treated 578xx as 57712.
This patch fixes the above and also removes unused data
structures.

Signed-off-by: Vladislav Zolotarov <vladz@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>