freedreno/ir3: move nop padding to legalize

freedreno/ir3: move nop padding to legalize

This way we can deal with it in one place, *after* all the blocks have
been scheduled.  Which will simplify life for a post-RA sched pass.

This has the benefit of already taking into account nop's that legalize
has to insert for non-delay related reasons.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3569>