asahi: Force linear for SHARED buffers with no/implicit modifier.
Consumers might not pass through the modifier information in this case.
Fixes XWayland/mutter using dma-buf v4 feedback (though the fact they try to use implicit modifiers is likely a bug on their end, and will decrease performance).
(Freedreno does the same thing here)
Signed-off-by: Asahi Lina lina@asahilina.net