[POWERPC] fix implicit declaration on cell.

(Only fails with -Werror-implicit-function-declaration, but
 it should still be fixed).

arch/powerpc/platforms/cell/setup.c:145: error: implicit declaration of function 'udbg_init_rtas_console'
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/cell/setup.c

@@ -49,6 +49,7 @@
 #include <asm/irq.h>
 #include <asm/spu.h>
 #include <asm/spu_priv1.h>
+#include <asm/udbg.h>
 
 #include "interrupt.h"
 #include "iommu.h"