tg3: Add more selfboot formats to NVRAM selftest

This patch adds more selfboot formats to the NVRAM selftest.  It also
changes the code to return an error on an unsupported NVRAM format.

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@conan.davemloft.net>