ac/nir/ngg: Wait for attribute stores before VS/TES/GS pos0 export.

ac/nir/ngg: Wait for attribute stores before VS/TES/GS pos0 export.

This is a HW bug workaround for some (all?) GFX11 chips.

On these chips, rasterization can start before the attribute ring
stores are finished, which can cause issues.
As a workaround, wait for attribute ring stores to finish
before doing the position export.

Mesh shaders will be taken care of in another commit.

Cc: mesa-stable
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24574>