x86: smpboot - check if we have ESR register in wakeup_secondary_cpu

We should check if we have ESR register before reading from it.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>