agx: Constant fold when optimizing int64

Otherwise we can get bcsel(false, ...) in the final optimized code, which isn't
great.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23480>

src/asahi/compiler/agx_compile.c

@@ -1966,6 +1966,7 @@ agx_optimize_nir(nir_shader *nir, unsigned *preamble_size)
          progress = false;
 
          NIR_PASS(progress, nir, nir_opt_algebraic);
+         NIR_PASS(progress, nir, nir_opt_constant_folding);
          NIR_PASS(progress, nir, nir_opt_dce);
       } while (progress);
    }