iris: assert that viewmask is 0

this is not supported by the driver, so it doesn't need to
be checked at runtime

Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31590>

src/gallium/drivers/iris/iris_context.h

@@ -1492,7 +1492,6 @@ iris_execute_indirect_draw_supported(const struct iris_context *ice,
    const struct iris_screen *screen = (struct iris_screen *)ice->ctx.screen;
    const struct iris_vs_data *vs_data =
       iris_vs_data(ice->shaders.prog[MESA_SHADER_VERTEX]);
-   const bool is_multiview = draw->view_mask != 0;
    const size_t struct_size = draw->index_size ?
       sizeof(uint32_t) * 5 :
       sizeof(uint32_t) * 4;
@@ -1503,7 +1502,6 @@ iris_execute_indirect_draw_supported(const struct iris_context *ice,
            aligned_stride &&
            (indirect &&
            !indirect->count_from_stream_output) &&
-           !is_multiview &&
            !(vs_data->uses_firstvertex ||
              vs_data->uses_baseinstance ||
              vs_data->uses_drawid));

src/gallium/drivers/iris/iris_state.c

@@ -3697,6 +3697,9 @@ iris_set_framebuffer_state(struct pipe_context *ctx,
    unsigned samples = util_framebuffer_get_num_samples(state);
    unsigned layers = util_framebuffer_get_num_layers(state);
 
+   /* multiview not supported */
+   assert(!state->viewmask);
+
    if (cso->samples != samples) {
       ice->state.dirty |= IRIS_DIRTY_MULTISAMPLE;