ir3/lower_parallelcopy: Use SWZ

ir3/lower_parallelcopy: Use SWZ

shader-db results on a650:

total instructions in shared programs: 1575484 -> 1574866 (-0.04%)
instructions in affected programs: 32579 -> 31961 (-1.90%)
helped: 75
HURT: 0
helped stats (abs) min: 1 max: 98 x̄: 8.24 x̃: 7
helped stats (rel) min: 0.41% max: 30.12% x̄: 2.47% x̃: 1.13%
95% mean confidence interval for instructions value: -10.97 -5.51
95% mean confidence interval for instructions %-change: -3.44% -1.51%
Instructions are helped.

total nops in shared programs: 355742 -> 355628 (-0.03%)
nops in affected programs: 18635 -> 18521 (-0.61%)
helped: 55
HURT: 147
helped stats (abs) min: 1 max: 14 x̄: 4.76 x̃: 6
helped stats (rel) min: 1.41% max: 100.00% x̄: 8.13% x̃: 4.76%
HURT stats (abs)   min: 1 max: 2 x̄: 1.01 x̃: 1
HURT stats (rel)   min: 0.56% max: 25.00% x̄: 2.09% x̃: 1.20%
95% mean confidence interval for nops value: -0.98 -0.15
95% mean confidence interval for nops %-change: -1.93% 0.55%
Inconclusive result (%-change mean confidence interval includes 0).

total non-nops in shared programs: 1219742 -> 1219238 (-0.04%)
non-nops in affected programs: 61125 -> 60621 (-0.82%)
helped: 220
HURT: 0
helped stats (abs) min: 1 max: 99 x̄: 2.29 x̃: 1
helped stats (rel) min: 0.19% max: 29.17% x̄: 0.90% x̃: 0.40%
95% mean confidence interval for non-nops value: -3.26 -1.32
95% mean confidence interval for non-nops %-change: -1.24% -0.56%
Non-nops are helped.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11565>