Normally when we shadow a resource (whether it is changing the modifier
or not) we do not need to flush existing batches, since they reference
the original version of the resource.  There is a special case for
resources that are referenced by a batches framebuffer state, because
this state is emitted when the batch is flushed.  Because of this, we
need those batches to be flushed before we shadow the resource.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <mesa/mesa!11371>