radeonsi: Put retile map in separate buffers.

radeonsi: Put retile map in separate buffers.

The retile maps are a software mechanism and hence very suceptible
to change. As such I'd like to avoid making it part of the cross
driver ABI.

Ideally we'd just use the cached tile info + a shader to avoid these
buffers altogether.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6783>