ACPICA: Add option to disable loading of SSDTs from the RSDT/XSDT

Optionally do not load any SSDTs from the RSDT/XSDT during
initialization.  This can be useful for overriding SSDTs
using DSDT overriding, thus useful for debugging ACPI
problems on some machines.  Lv Zheng. ACPICA BZ 1005.

References: https://bugs.acpica.org/show_bug.cgi?id=1005
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>