cpus: Add a macro to walk CPUs in reverse

Add CPU_FOREACH_REVERSE that walks CPUs in reverse.

Needed for PowerPC CPU device tree reorganization.
Signed-off-by: NBharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAlexander Graf <agraf@suse.de>

include/qom/cpu.h

@@ -323,6 +323,8 @@ extern struct CPUTailQ cpus;
 #define CPU_FOREACH(cpu) QTAILQ_FOREACH(cpu, &cpus, node)
 #define CPU_FOREACH_SAFE(cpu, next_cpu) \
     QTAILQ_FOREACH_SAFE(cpu, &cpus, node, next_cpu)
+#define CPU_FOREACH_REVERSE(cpu) \
+    QTAILQ_FOREACH_REVERSE(cpu, &cpus, CPUTailQ, node)
 #define first_cpu QTAILQ_FIRST(&cpus)
 
 DECLARE_TLS(CPUState *, current_cpu);