aco: use Builder::copy more

aco: use Builder::copy more

fossil-db (Navi):
Totals from 6973 (5.07% of 137413) affected shaders:
SGPRs: 381768 -> 381776 (+0.00%)
VGPRs: 306092 -> 306096 (+0.00%); split: -0.00%, +0.00%
CodeSize: 24440844 -> 24421196 (-0.08%); split: -0.09%, +0.01%
MaxWaves: 86581 -> 86583 (+0.00%)
Instrs: 4682161 -> 4679578 (-0.06%); split: -0.06%, +0.00%
Cycles: 68793116 -> 68261648 (-0.77%); split: -0.83%, +0.05%

fossil-db (Polaris):
Totals from 8154 (5.87% of 138881) affected shaders:
VGPRs: 338916 -> 338920 (+0.00%); split: -0.00%, +0.00%
CodeSize: 23540428 -> 23540488 (+0.00%); split: -0.00%, +0.00%
MaxWaves: 49090 -> 49091 (+0.00%)
Instrs: 4576085 -> 4576101 (+0.00%); split: -0.00%, +0.00%
Cycles: 51720704 -> 51720888 (+0.00%); split: -0.00%, +0.00%

Most of the Navi cycle/instruction changes are from 8/16-bit parallel-rdp
shaders. They appear to be improved because the p_create_vector from
lower_subdword_phis() was blocking constant propagation.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7216>