anv: Use nir_opt_barrier_modes() to drop unnecessary barriers

anv: Use nir_opt_barrier_modes() to drop unnecessary barriers

fossil-db stats on Alchemist:

   Totals:
   Instrs: 196514947 -> 196513342 (-0.00%); split: -0.00%, +0.00%
   Cycles: 14271450761 -> 14271426028 (-0.00%); split: -0.00%, +0.00%
   Send messages: 8022316 -> 8021892 (-0.01%)

   Totals from 43 (0.01% of 653252) affected shaders:
   Instrs: 98558 -> 96953 (-1.63%); split: -1.63%, +0.00%
   Cycles: 15867801 -> 15843068 (-0.16%); split: -0.17%, +0.02%
   Send messages: 8997 -> 8573 (-4.71%)

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24842>