freedreno/ir3: add a pass to collect SSA uses

freedreno/ir3: add a pass to collect SSA uses

We don't really track these as the ir is transformed, but it would be a
useful thing for some passes to have.  So add a pass to collect this
information.  It uses instr->data (generic per-pass ptr), with the
hashsets hanging under a mem_ctx for easy disposal at the end of the
pass.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4423>