This patch adds a .notify() method.  The presence of .notify() causes
Linux/ACPI to manage event handlers and notify handlers on our behalf,
so we don't have to install and remove them ourselves.

This driver relies on seeing system notify events, not device-specific
ones (because it used ACPI_SYSTEM_NOTIFY).  We use the
ACPI_DRIVER_ALL_NOTIFY_EVENTS driver flag to request all events, then
just ignore any device events we get.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
CC: Corentin Chary <corentincj@iksaif.net>
CC: acpi4asus-user@lists.sourceforge.net
CC: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>