vl: Make -machine $TYPE,help and -accel help print to stdout

Command line help help explicitly requested by the user should be
printed to stdout, not stderr.  We do elsewhere.  Adjust -machine
$TYPE,help and -accel help to match: use printf() instead of
error_printf().

Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Message-Id: <20190417190641.26814-10-armbru@redhat.com>

vl.c

@@ -1556,12 +1556,12 @@ static int machine_help_func(QemuOpts *opts, MachineState *machine)
             continue;
         }
 
-        error_printf("%s.%s=%s", MACHINE_GET_CLASS(machine)->name,
-                     prop->name, prop->type);
+        printf("%s.%s=%s", MACHINE_GET_CLASS(machine)->name,
+               prop->name, prop->type);
         if (prop->description) {
-            error_printf(" (%s)\n", prop->description);
+            printf(" (%s)\n", prop->description);
         } else {
-            error_printf("\n");
+            printf("\n");
         }
     }
 
@@ -3643,7 +3643,7 @@ int main(int argc, char **argv, char **envp)
                                                      optarg, true);
                 optarg = qemu_opt_get(accel_opts, "accel");
                 if (!optarg || is_help_option(optarg)) {
-                    error_printf("Possible accelerators: kvm, xen, hax, tcg\n");
+                    printf("Possible accelerators: kvm, xen, hax, tcg\n");
                     exit(0);
                 }
                 opts = qemu_opts_create(qemu_find_opts("machine"), NULL,