iris: Apply the flushes when switching pipelines.

iris: Apply the flushes when switching pipelines.

Even though the workaround description says:

   "all the listed commands are non-pipelined and hence flush caused due
   to pipeline mode change must not cause performance issues..."

My understanding is that we still need to have the flushes. Also, the
flushes are required not only to stall the pipeline, but also to clear
caches, so I don't think they can simply be discarded.

Additionally, while doing some testing that increased the number of
surface STATE_BASE_ADDRESS emitted, I got a lot more GPU hangs. Adding
these flushes fixes those hangs.

Fixes: b8fbb39a (iris: Implement Gen12 workaround for non pipelined
                 state)

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3908>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3908>