e100: Do suspend/shutdown like e1000

This fixes a "trying to free already free IRQ" message and simplifies
the shutdown/suspend code by re-using already existing code when going
to suspend. The code is now symmetric with e100_resume.

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>