anv: Flatten descriptor bindings in anv_nir_apply_pipeline_layout

This lets us stop tracking the pipeline layout.  It also means less
indirection on a very hot path.  As an extra bonus, we can make some of
our data structures smaller.  No measurable CPU overhead improvement.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/vulkan/genX_pipeline.c

@@ -1111,7 +1111,6 @@ emit_cb_state(struct anv_pipeline *pipeline,
          continue;
       }
 
-      assert(binding->binding == 0);
       const VkPipelineColorBlendAttachmentState *a =
          &info->pAttachments[binding->index];