tg3: Extract FW ver from alt NVRAM formats

This patch extracts the bootcode firmware version from the alternate
selfboot patch NVRAM format.  This format is used on the 5784, 5761 and
some newer devices.

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>