MIPS: Use common outgoing-CPU-notification code

Replace the open-coded CPU-offline notification with common code.
In particular avoid calling scheduler code using RCU from an offline CPU
that RCU is ignoring.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15921/
Patchwork: https://patchwork.linux-mips.org/patch/15953/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>