zdump/stdout: Extract stdout.h header from zgetdump.h

Create a separate C header for STDOUT to separate independent things and
make it more readable.

Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdump/stdout.h

@@ -0,0 +1,13 @@
+/*
+ * Copyright IBM Corp. 2001, 2018
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#ifndef STDOUT_H
+#define STDOUT_H
+
+int stdout_write_dump(void);
+
+#endif /* STDOUT_H */