MIPS: Octeon: Mark some functions __init in smp.c

MIPS: Octeon: Mark some functions __init in smp.c

octeon_smp_setup and octeon_prepare_cpus are just used during initialization
period, so mark them as __init. And, octeon_prepare_cpus is just used in smp.c,
so make it static as well.

Signed-off-by: Yang Shi <yang.shi@windriver.com>
Cc: david.daney@cavium.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12574/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>