zink: add more explicit fencing for transfer maps

we're using our (primitive) buffer r/w tracking here to ensure that our
src buffers are synchronized before we do any kind of read operation on them

this is pretty slow in some cases, but it fixes a bunch of piglit tests

Reviewed-by: Erik Faye-Lun <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6924>
1 file changed