tg3: fix warnings

In case CONFIG_PM_SLEEP is disabled, we dont need tg3_suspend() and
tg3_resume().

drivers/net/tg3.c:15056: warning: ‘tg3_suspend’ defined but not used
drivers/net/tg3.c:15110: warning: ‘tg3_resume’ defined but not used

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Michael Chan <mchan@broadcom.com>
Cc: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>