x86/smpboot: Move data structure to its primary usage scope

Makes the code more readable by moving variable and usage closer
to each other, which also avoids this build warning in the
!CONFIG_HOTPLUG_CPU case:

  arch/x86/kernel/smpboot.c:105:42: warning: ‘die_complete’ defined but not used [-Wunused-variable]

Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Lan Tianyu <tianyu.lan@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: srostedt@redhat.com
Cc: toshi.kani@hp.com
Cc: imammedo@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409039025-32310-1-git-send-email-tianyu.lan@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>