pseries: Increase maximum CPUs to 256

The original pSeries machine was limited to 32 CPUs, more or less
arbitrarily.  Particularly when we get SMT KVM guests it will be
pretty easy to exceed this.  Therefore, raise the max number of CPUs
in a pseries machine guest to 256.

Signed-off-by: Anton Blanchard <anton@au1.ibm.com>
Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

hw/spapr.c

@@ -51,7 +51,7 @@
 
 #define TIMEBASE_FREQ           512000000ULL
 
-#define MAX_CPUS                32
+#define MAX_CPUS                256
 #define XICS_IRQS		1024
 
 sPAPREnvironment *spapr;