m32r: fix build due to notify_cpu_starting() change

fix:

arch/m32r/kernel/smpboot.c:501: err
or: implicit declaration of function 'notify_cpu_starting'
make[2]: *** [arch/m32r/kernel/smpboot.o] Error 1
make[2]: *** Waiting for unfinished jobs....
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/m32r/kernel/smpboot.c

@@ -40,6 +40,7 @@
  */
 
 #include <linux/module.h>
+#include <linux/cpu.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>