ACPI / scan: Avoid enumerating devices more than once

acpi_bus_attach() does not check the visited flag for devices that
have been enumerated already and some of them may be enumerated
for multiple times as a result, because some callers of
acpi_bus_scan() don't check the visited flag either.

For this reason, modify acpi_bus_attach() to check the visited flag
and avoid enumerating devices that have already been enumerated.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Joey Lee <jlee@suse.com>