MIPS: OCTEON: support disabling HOTPLUG_CPU run-time

If nosmp kernel option given, we can assume HOTPLUG_CPU is disabled.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7202/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>