target/ppc: Simplify cpu valid check in ppc_cpu_realize

The #if isn't necessary, because there's a suitable one inside
ppc_cpu_is_valid().  We've already filtered for suitable cpu models in the
functions that search and register them.  So by the time we get to realize
having an invalid one indicates a code error, not a user error, so an
assert() is more appropriate than error_setg().
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NGreg Kurz <groug@kaod.org>

target/ppc/translate_init.c

@@ -9749,14 +9749,7 @@ static void ppc_cpu_realize(DeviceState *dev, Error **errp)
         }
     }
 
-#if defined(TARGET_PPCEMB)
-    if (!ppc_cpu_is_valid(pcc)) {
-        error_setg(errp, "CPU does not possess a BookE or 4xx MMU. "
-                   "Please use qemu-system-ppc or qemu-system-ppc64 instead "
-                   "or choose another CPU model.");
-        goto unrealize;
-    }
-#endif
+    assert(ppc_cpu_is_valid(pcc));
 
     create_ppc_opcodes(cpu, &local_err);
     if (local_err != NULL) {