powerpc: Make some #includes explicit.

In preparation for merging processor.h, this adds some explicit
but won't be after the merge.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/ppc/kernel/smp.c b/arch/ppc/kernel/smp.c
index a8cc96b..801c793 100644
--- a/arch/ppc/kernel/smp.c
+++ b/arch/ppc/kernel/smp.c
@@ -34,6 +34,7 @@
 #include <asm/thread_info.h>
 #include <asm/tlbflush.h>
 #include <asm/xmon.h>
+#include <asm/machdep.h>
 
 volatile int smp_commenced;
 int smp_tb_synchronized;