PNPACPI: Add support for remote wakeup

This patch (as1354) adds remote-wakeup support to the pnpacpi driver.
The new can_wakeup method also allows other PNP protocol drivers
(pnpbios or iaspnp) to add wakeup support, but I don't know enough
about how they work to actually do it.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reviewed-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>