[POWERPC] PS3: Fix CONFIG_SMP=n, CONFIG_KEXEC=y build

Currently, the ps3 kernel fails to build without smp but with kexec, as
ps3_kexec_cpu_down needs ps3_smp_cleanup_cpu, which isn't defined on UP
kernels. This change adds an empty ps3_smp_cleanup_cpu for UP kernels.

Booted on ps3.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/ps3/platform.h

@@ -47,7 +47,11 @@ void __init ps3_register_ipi_debug_brk(unsigned int cpu, unsigned int virq);
 /* smp */
 
 void smp_init_ps3(void);
+#ifdef CONFIG_SMP
 void ps3_smp_cleanup_cpu(int cpu);
+#else
+static inline void ps3_smp_cleanup_cpu(int cpu) { }
+#endif
 
 /* time */