ACPICA: Revert "iASL: change processing of external op namespace nodes for correctness"

Revert commit b43eac6f (ACPICA: iASL: change processing of
external op namespace nodes for correctness; upstream ACPICA
commit aa866a9b4f24bbec9f158d10325b486d7d12d90f).

This was done in order to allow more relaxed usage of ASL external
declarations.

Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>