e100: rework WoL and shutdown handling

Unify our shutdown/suspend/resume code and make it similar to e1000:
e1000_shutdown now calls suspend which does the exact same thing on
shutdown except saving PCI config state on suspend. WoL setup code
is now also more simple and works even when CONFIG_PM is not set, which
was previously broken.

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>