r600: Fix reading back from a temp array immediately after writing on RV770.

r600: Fix reading back from a temp array immediately after writing on RV770.

KHR-GL33.shaders.indexing.tmp_array.vertexid regressed with the switch to
NIR-to-TGSI because the shader got optimized enough to emit a read just
after writing to the array (the kind of situation where a non-rel write
would have been followed by a PV/PS read).  The R600 and EG docs say you
always need to do this, but apparently some hardware gives you the right
answer anyway so we don't flag it on all of them.

Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14319>