tg3: Fix SEEPROM accesses

The recent NVRAM patches sanitized how the driver deals with NVRAM
data, but they failed to bring the SEEPROM interfaces inline with
the new strategy.  This patch brings the SEEPROM interfaces up to date.
This patch also reverts commit 0d489ffb
("tg3: fix big endian MAC address collection failure").

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Tested-by: Robin Holt <holt@sgi.com>
Tested-by: James Bottomley <james.bottomley@HansenPartnership.com>
Signed-off-by: David S. Miller <davem@davemloft.net>