ACPI: Reduce acpi_bind_one()/acpi_unbind_one() code duplication

Move some duplicated code from acpi_bind_one() and acpi_unbind_one()
into a separate function and make that function use snprintf()
instead of sprintf() for extra safety.

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