tg3: Add support for extended VPD blocks

In some devices, the VPD block is relocated to a different area in
NVRAM.  The original location can still contain old, but still valid VPD
data.  This patch changes the code to look for an extended VPD block in
NVRAM.  If one is found, that block is used for all VPD operations
instead.

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