freedreno/a6xx+ir3: stop generating pointless binning shaders

freedreno/a6xx+ir3: stop generating pointless binning shaders

Currently we always do sysmem if there is tess.  And for GS, the binning
pass VS ends up identical to the draw pass VS, so no point in compiling
it twice.  (For GS what we should do someday is generate a binning pass
GS, and possibly if we can do cross-stage linking opts, an optimized
binning pass VS, but the required outputs would somehow have to end up
in the shader variant key.)

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5372>