block/raw-win32: create one QEMUWin32AIOState per BDRVRawState

Each QEMUWin32AIOState event notifier is associated with an AioContext.
Since BlockDriverState instances can use different AioContexts we cannot
continue to use a global QEMUWin32AIOState.

Let each BDRVRawState have its own QEMUWin32AIOState and free it when
BDRVRawState is closed.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/win32-aio.c

@@ -204,3 +204,11 @@ out_free_state:
     g_free(s);
     return NULL;
 }
+
+void win32_aio_cleanup(QEMUWin32AIOState *aio)
+{
+    qemu_aio_set_event_notifier(&aio->e, NULL);
+    CloseHandle(aio->hIOCP);
+    event_notifier_cleanup(&aio->e);
+    g_free(aio);
+}