x86: smpboot - wakeup_secondary should be done via __cpuinit section

A caller (do_boot_cpu) already has __cpuinit attribute.

Since HOTPLUG_CPU depends on SMP && HOTPLUG it doesn't
lead to panic at moment.

[ Impact: cleanup ]

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
LKML-Reference: <20090418194528.GD25510@lenovo>
Signed-off-by: Ingo Molnar <mingo@elte.hu>