turnip: rework streamout state and add missing counter buffer read/writes

turnip: rework streamout state and add missing counter buffer read/writes

Rework the streamout state and at the same time fix some issues, the
biggest one being to actually use the counter buffers instead of ignoring
them completely.

(note it appears the dEQP tests are bad and able to pass with the previous
broken behavior of not ever reading/writing from the counter buffers)

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5579>