[TG3]: Fix nvram selftest failures

Newer devices contain bootcode in the chip's private ROM area.  This
bootcode is called selfboot.  Selfboot can be patched in the device's
NVRAM and the patches can have several formats.  In one particular
format, the checksum calculation needs to be slightly modified.  This
patch adjusts the NVRAM test code for that case, and add support for the
missing formats.

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>