ACPI: Remove unused lockable in acpi_device_flags

Removed lockable in struct acpi_device_flags since it is no
longer used by any code. acpi_bus_hot_remove_device() cannot
use this flag because acpi_bus_trim() frees up its acpi_device
object. Furthermore, the dock driver calls _LCK method without
using this lockable flag.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>