[why]
stream ID allows DMs to avoid memory address comparisons to compare
stream equality.
otg_instance allows DC to more rigorously define when otg_instance
can change.  specifically, it is now defined to be only mutable when dc_stream_state
changes.  This is better than a "get status" function which prevents efficient
caching of otherwise very stable information.

[how]
stream ID follows similar pattern to sink ID, which is already implemented

otg_instance is an output which occurs on all dc_stream modification functions
Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>