qapi: ignore generated event files

Signed-off-by: NWenchao Xia <wenchaoqemu@gmail.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

.gitignore

@@ -26,6 +26,7 @@
 /qapi-generated
 /qapi-types.[ch]
 /qapi-visit.[ch]
+/qapi-event.[ch]
 /qmp-commands.h
 /qmp-marshal.c
 /qemu-doc.html