nir: Rename nir_intrinsic_barrier to control_barrier

This is a more explicit name now that we don't want it to be doing any
memory barrier stuff for us.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3307>
18 files changed