powerpc/crash: Fix build error without SMP

I could not find cpus_in_crash anywhere in the sourcetree, except for
arch/powerpc/kernel/crash.c. Moving the definition into the CONFIG_SMP
fixes it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/crash.c b/arch/powerpc/kernel/crash.c
index 28be345..abef7517 100644
--- a/arch/powerpc/kernel/crash.c
+++ b/arch/powerpc/kernel/crash.c
@@ -46,7 +46,6 @@
 /* This keeps a track of which one is the crashing cpu. */
 int crashing_cpu = -1;
-static atomic_t cpus_in_crash;
 static int time_to_dump;
@@ -66,6 +65,7 @@
 #ifdef CONFIG_SMP
+static atomic_t cpus_in_crash;
 void crash_ipi_callback(struct pt_regs *regs)
 	static cpumask_t cpus_state_saved = CPU_MASK_NONE;