radeonsi: Do not try to disable displayable DCC with modifiers.

radeonsi: Do not try to disable displayable DCC with modifiers.

We do flushing on glFlush etc., so we don't need explicit flush,
but we still need to avoid frontbuffer rendering.

For modifiers there was logic put in apps that basically prevent
frontbuffer rendering if multipe planes are involved.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6176>