MIPS: SMTC: delay irq enable to ->smp_finish()

To prepare for smoothing set_cpu_[active|online]() mess up

Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Cc: Sergei Shtylyov <sshtylyov@mvista.com>
Cc: David Daney <david.daney@cavium.com>
Acked-by: David Daney <david.daney@cavium.com>
Patchwork: https://patchwork.linux-mips.org/patch/3847/


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