freedreno/a6xx: only generate streamout for draw pass shader

freedreno/a6xx: only generate streamout for draw pass shader

Previously we were doing this both for draw and binning pass.. resulting
that the stateobj contained first the incorrect state (based on binning
pass shader with varyings DCEd) followed by the correct state.

Also, in the streamout case we should link binning pass VS against the
real FS, rather than the dummy FS, so that OUTLOC's match (since same
streamout stateobj is used for both draw and binning pass).

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6376>