ARM: rockchip: ensure CPU to enter WFI/WFE state

The patch can ensure that v7_exit_coherency_flush() in rockchip_cpu_die()
executed in time.
The mdelay(1) has enough time to fix the problem of CPU offlining.
That's a workaround way in rockchip hotplug code,
At least, we haven't a better way to solve it. Who know,
that maybe fixed by chip (hardware) in the future.

Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>