ACPICA: Linux header: Add support for stubbed externals.

Linux wants to include all header files but leave empty inline
stub variables for a feature that is not configured during build.

This patch configures ACPICA external globals/macros/functions out and
defines them into no-op when CONFIG_ACPI is not enabled.  Lv Zheng.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>