nir: Add a new lowering option to lower 3D surfaces from txd to txl.

Tested on gen9.

v2: Rename lower_txd_3d_surafaces flag to lower_txd_3d (Jason Ekstrand)

Signed-off-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/nir/nir.h

@@ -3008,6 +3008,11 @@ typedef struct nir_lower_tex_options {
     */
    bool lower_txd_cube_map;
 
+   /**
+    * If true, lower nir_texop_txd on 3D surfaces with nir_texop_txl.
+    */
+   bool lower_txd_3d;
+
    /**
     * If true, lower nir_texop_txd on shadow samplers (except cube maps)
     * with nir_texop_txl. Notice that cube map shadow samplers are lowered