asahi: Assume LAYER is flat-shaded

It can't be anything else, this makes sure the varyings are sorted properly.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>

src/asahi/compiler/agx_compile.c

@@ -2371,6 +2371,9 @@ agx_remap_varyings_vs(nir_shader *nir, struct agx_varyings_vs *varyings,
    varyings->slots[VARYING_SLOT_POS] = base;
    base += 4;
 
+   /* These are always flat-shaded from the FS perspective */
+   key->vs.outputs_flat_shaded |= VARYING_SLOT_LAYER | VARYING_SLOT_VIEWPORT;
+
    assert(!(key->vs.outputs_flat_shaded & key->vs.outputs_linear_shaded));
 
    /* Smooth 32-bit user bindings go next */