ACPI: support acpi_device_ops .notify methods

This patch adds support for ACPI device driver .notify() methods.  If
such a method is present, Linux/ACPI installs a handler for device
notifications (but not for system notifications such as Bus Check,
Device Check, etc).  When a device notification occurs, Linux/ACPI
passes it on to the driver's .notify() method.

In most cases, this removes the need for drivers to install their own
handlers for device-specific notifications.

For fixed hardware devices like some power and sleep buttons, there's
no notification value because there's no control method to execute a
Notify opcode.  When a fixed hardware device generates an event, we
handle it the same as a regular device notification, except we send
a ACPI_FIXED_HARDWARE_EVENT value.  This is outside the normal 0x0-0xff
range used by Notify opcodes.

Several drivers install their own handlers for system Bus Check and
Device Check notifications so they can support hot-plug.  This patch
doesn't affect that usage.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Reviewed-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>