Modify acpi_bus_type so that it executes PM callbacks provided
by drivers through their struct dev_pm_ops objects, if present,
while still allowing the legacy ACPI PM callbacks to take precedence.
This will make it possible to convert ACPI drivers one by one to
handling PM through struct dev_pm_ops instead of the legacy way.

The code added by this change is temporary and will be removed
when all of the drivers in question have been switched over to
the PM handling based on struct dev_pm_ops.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>