broadcom/vc5: Enable NIR txd lowering on all txd instructions.

Fixes almost all of piglit's arb_shader_texture_lod grad tests, except for
the base -texgrad/texgradcube ones which fail on what appear to be
precision problems.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/broadcom/compiler/vir.c

@@ -541,6 +541,7 @@ static void
 v3d_lower_nir(struct v3d_compile *c)
 {
         struct nir_lower_tex_options tex_options = {
+                .lower_txd = true,
                 .lower_rect = false, /* XXX */
                 .lower_txp = ~0,
                 /* Apply swizzles to all samplers. */