freedreno/ir3/ra: compute register target from liveranges

freedreno/ir3/ra: compute register target from liveranges

Using the output of the first pass isn't ideal, as it can bake in the
losses from fragmentation which the scalar pass is intended to fill in.
This gets worse when we start using "vectorish" instructions, due to
higher use of vecN values.

Instead, we can just use the outputs of the liveness analysis to get a
more accurate # of maximum live values at any point.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4272>