gallium: add a non-multisample sample mask out behaviour flag.

Vulkan/DX want to use output sample mask even when not multisampling
GL wants it ignored.

Add a rasterizer flag to lavapipe can get correct behaviour.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7435>
diff --git a/src/gallium/include/pipe/p_state.h b/src/gallium/include/pipe/p_state.h
index 0ae0297..fbf4636 100644
--- a/src/gallium/include/pipe/p_state.h
+++ b/src/gallium/include/pipe/p_state.h
@@ -111,6 +111,7 @@
    unsigned point_tri_clip:1; /** large points clipped as tris or points */
    unsigned point_size_per_vertex:1; /**< size computed in vertex shader */
    unsigned multisample:1;         /* XXX maybe more ms state in future */
+   unsigned no_ms_sample_mask_out;
    unsigned force_persample_interp:1;
    unsigned line_smooth:1;
    unsigned line_stipple_enable:1;