ACPI / scan: Add bind/unbind callbacks to struct acpi_scan_handler

In some cases it may be necessary to perform certain setup/cleanup
operations on a device object representing a physical device after
it has been associated with an ACPI companion by acpi_bind_one() or
before disassociating it from that companion by acpi_unbind_one(),
respectively.  If there is a struct acpi_bus_type object for the
given device's bus type, the .setup()/.cleanup() callbacks from there
are executed for these purposes.  However, an analogous mechanism will
be necessary for devices whose bus types don't have corresponding
struct acpi_bus_type objects and that have specific ACPI scan handlers.

For those devices, add new .bind() and .unbind() callbacks to struct
acpi_scan_handler that will be executed by acpi_platform_notify()
right after the given device has been associated with an ACPI
comapnion and by acpi_platform_notify_remove() right before calling
acpi_unbind_one() for that device, respectively.

To make that work for scan handlers registering new devices in their
.attach() callbacks, modify acpi_scan_attach_handler() to set the
ACPI device object's handler field before calling .attach() from the
scan handler at hand.

This changeset includes a fix from Mika Westerberg.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>