Net / e1000e: Fix build issue introduced by runtime PM patch

The recent PCI runtime PM patch broke build for CONFIG_PM_RUNTIME
and CONFIG_PM_SLEEP undefined.  Fix that by moving the PM callbacks
under suitable #ifdefs.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>