qapi event: convert POWERDOWN

There is no existing comments for POWERDOWN in doc/qmp/qmp-events.txt,
so no change on it like other conversion patch.

Signed-off-by: Wenchao Xia <wenchaoqemu@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

qapi-event.json

diff --git a/qapi-event.json b/qapi-event.json
index 7a6e6bf..ca08289 100644
--- a/qapi-event.json
+++ b/qapi-event.json
@@ -10,3 +10,13 @@
 # Since: 0.12.0
 ##
 { 'event': 'SHUTDOWN' }
+
+##
+# @POWERDOWN
+#
+# Emitted when the virtual machine is powered down through the power control
+# system, such as via ACPI.
+#
+# Since: 0.12.0
+##
+{ 'event': 'POWERDOWN' }

vl.c

diff --git a/vl.c b/vl.c
index 1d82b12..abb56d3 100644
--- a/vl.c
+++ b/vl.c
@@ -1932,7 +1932,7 @@
 
 static void qemu_system_powerdown(void)
 {
-    monitor_protocol_event(QEVENT_POWERDOWN, NULL);
+    qapi_event_send_powerdown(&error_abort);
     notifier_list_notify(&powerdown_notifiers, NULL);
 }