Fix possible fault for methods that optionally have no return value.

Currently applies to the _WAK method only. If the method has no return
value and slack mode is not enabled, the return value validation code
can fault.

Also improves the error message when an expected return value is
missing (for any predefined name/method).
iASL: Add support for One/Ones/Zero opcodes for the -so option.

Emits an offset entry for Name() objects that are initialized
with these AML opcodes.