freedreno/ir3: handle the progress case

freedreno/ir3: handle the progress case

In some cases, in particular when you have things that can be src
modifiers ((abs)/(neg)), once eliminating one mov, there is a
possibility to remove another.  Handle this by re-visiting an
instruction after eliminating a copy on one of it's srcs.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>