tg3: Use VPD fw version when present

This patch extracts the firmware version from the VPD area and changes
the code to prefer that version version over the manually extracted
version.

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>