i965/nir: enable lowering of texture gradient for shadow samplers

This gets the lowering on the Vulkan driver too, which is required for
hardware that does not have the sample_l_d message (up to IvyBridge).

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
diff --git a/src/mesa/drivers/dri/i965/brw_nir.c b/src/mesa/drivers/dri/i965/brw_nir.c
index f6bcd45..55b16cf 100644
--- a/src/mesa/drivers/dri/i965/brw_nir.c
+++ b/src/mesa/drivers/dri/i965/brw_nir.c
@@ -596,6 +596,9 @@
          tex_options.swizzles[s][c] = GET_SWZ(key_tex->swizzles[s], c);
    }
 
+   /* Prior to Haswell, we have to lower gradients on shadow samplers */
+   tex_options.lower_txd_shadow = devinfo->gen < 8 && !devinfo->is_haswell;
+
    tex_options.lower_y_uv_external = key_tex->y_uv_image_mask;
    tex_options.lower_y_u_v_external = key_tex->y_u_v_image_mask;
    tex_options.lower_yx_xuxv_external = key_tex->yx_xuxv_image_mask;