iris: don't synchronize BO for batch decoding

iris: don't synchronize BO for batch decoding

We don't need to go to the kernel to synchronize the BO we want to
decode with INTEL_DEBUG=bat, mostly because we'll decode what was
written by the driver in the batch.

This also works around an issue in the simulation environment.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 9ac81f189050 ("iris: decoder fixes")
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15517>