api: Add a header for api_init()

Put this in its own header instead of using common.h.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/api.h b/include/api.h
new file mode 100644
index 0000000..85817f3
--- /dev/null
+++ b/include/api.h
@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2017 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#ifndef __API_H
+#define __API_H
+
+void api_init(void);
+
+#endif