cpu: Use ppc64Compute() to implement ppc64DriverCompare()

This ensures comparison of two CPU definitions will be consistent
regardless of the fact that it is performed using cpuCompare() or
cpuGuestData(). The x86 driver uses the same exact code.

src/cpu/cpu_ppc64.c

@@ -438,16 +438,22 @@ ppc64DriverCompare(virCPUDefPtr host,
                    virCPUDefPtr cpu,
                    bool failIncompatible)
 {
-    if ((cpu->arch == VIR_ARCH_NONE || host->arch == cpu->arch) &&
-        STREQ(host->model, cpu->model))
-        return VIR_CPU_COMPARE_IDENTICAL;
+    virCPUCompareResult ret;
+    char *message = NULL;
 
-    if (failIncompatible) {
-        virReportError(VIR_ERR_CPU_INCOMPATIBLE, NULL);
-        return VIR_CPU_COMPARE_ERROR;
-    } else {
-        return VIR_CPU_COMPARE_INCOMPATIBLE;
+    ret = ppc64Compute(host, cpu, NULL, &message);
+
+    if (failIncompatible && ret == VIR_CPU_COMPARE_INCOMPATIBLE) {
+        ret = VIR_CPU_COMPARE_ERROR;
+        if (message) {
+            virReportError(VIR_ERR_CPU_INCOMPATIBLE, "%s", message);
+        } else {
+            virReportError(VIR_ERR_CPU_INCOMPATIBLE, NULL);
+        }
     }
+    VIR_FREE(message);
+
+    return ret;
 }
 
 static int