[AMD] NFC: Refactor stream pipeliner to better encapsulate functions (#7540)

Mostly moves code around to reduce the dependencies between functions
and further splits up functions doing more than one thing
(`createAndSchedule*`,` preprocessAndBuildSchedule`). This will also
allow us to use more common pipeliner functionality in a future PR, e.g.
`createAsyncCopy`.

Author: AlexAUT