ACPICA: Remove possibility of executing _REG methods twice

If a custom address space handler is installed by the host
before the "initialize operation regions" phase of the ACPICA
initialization, any _REG methods for that address space could
be executed twice. This change fixes the problem.
ACPICA BZ 427.

http://www.acpica.org/bugzilla/show_bug.cgi?id=427

Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>