ACPI / hotplug / PCI: Use acpi_handle_debug() in hotplug_event()

Make hotplug_event() use acpi_handle_debug() instead of an open-coded
debug message printing and clean up the messages printed by it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>