[TG3]: Add new 5761 NVRAM decode routines

This patch adds a new 5761-specific NVRAM strapping decode routine.

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