The async implementation is inconsistent in terms of the assembly
format. While renaming `UpdateOp`'s `async` to `asyncOnly`, this PR
handles `asyncOnly` along with async operands in every operation.
Regarding `EnterDataOp` and `ExitDataOp`, they do not accept device
types; thus, the async and the wait clauses without values lead to the
`async` and the `wait` attributes (not `asyncOnly` nor `waitOnly`). This
PR also processes them with async and wait operands all together.
f9dbfb1566