radv,aco: compact vertex buffer descriptors

It seems common for there to be holes.

fossil-db (GFX10.3, robustBufferAccess enabled):
Totals from 33791 (23.10% of 146267) affected shaders:
(no statistics changed)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7871>

src/amd/vulkan/radv_nir_to_llvm.c

@@ -758,6 +758,8 @@ handle_vs_input_decl(struct radv_shader_context *ctx, struct nir_variable *varia
 
       unsigned desc_index =
          ctx->args->shader_info->vs.use_per_attribute_vb_descs ? attrib_index : attrib_binding;
+      desc_index = util_bitcount(ctx->args->shader_info->vs.vb_desc_usage_mask &
+                                 u_bit_consecutive(0, desc_index));
       t_offset = LLVMConstInt(ctx->ac.i32, desc_index, false);
       t_list = ac_build_load_to_sgpr(&ctx->ac, t_list_ptr, t_offset);