freedreno/ir3/ra: fix array conflicts for split/merged

freedreno/ir3/ra: fix array conflicts for split/merged

Properly handle the difference between split and merged register file
when determining where arrays can fit without conflicting with other
arrays or pre-colored instructions.

1) if not mergedregs, only consider other things with same precision
   as potentially conflicting
2) if mergedregs, calculate everything in therms of half-regs and
   convert back to fullregs in the end

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5957>