pnp: add a shutdown method to pnp drivers

The shutdown method is used by the winbond cir driver to setup the
hardware for wake-from-S5.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: David Härdeman <david@hardeman.nu>
Cc: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>