ac/nir/ngg: Wait for attribute ring stores in mesh shaders.

ac/nir/ngg: Wait for attribute ring stores in mesh shaders.

Make sure that both per-vertex and per-primitive attribute
ring stores are finished before position or primitive export
instructions are executed.

This is necessary because we need to ensure that mesh shader
waves work correctly when they have either vertex-only or
primitive-only waves.

Cc: mesa-stable
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24574>