ACPICA: Enhance implicit return mechanism

For Windows compatibility, return an implicit integer of value
zero for methods that have no executable code. A default implicit
value of zero is provided for methods. Lin Ming.

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>