Disintegrate asm/system.h for PowerPC

Disintegrate asm/system.h for PowerPC.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
cc: linuxppc-dev@lists.ozlabs.org
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index a50b5ec..2692efd 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -33,6 +33,7 @@
 #include <asm/cacheflush.h>
 #include <asm/syscalls.h>
 #include <asm/vdso.h>
+#include <asm/switch_to.h>
 
 #include "signal.h"