aco: keep can_reorder/barrier when combining addition into SMEM

aco: keep can_reorder/barrier when combining addition into SMEM

Affects 30 shaders in the pipeline-db (all youngblood).

Totals from affected shaders:
SGPRS: 2656 -> 2456 (-7.53 %)
VGPRS: 2260 -> 2260 (0.00 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 240680 -> 240944 (0.11 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 90 -> 90 (0.00 %)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>