s390/kexec_file: Add purgatory

The common code expects the architecture to have a purgatory that runs
between the two kernels. Add it now. For simplicity first skip crash
support.

Signed-off-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/purgatory.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright IBM Corp. 2018
+ *
+ * Author(s): Philipp Rudo <prudo@linux.vnet.ibm.com>
+ */
+
+#ifndef _S390_PURGATORY_H_
+#define _S390_PURGATORY_H_
+#ifndef __ASSEMBLY__
+
+#include <linux/purgatory.h>
+
+int verify_sha256_digest(void);
+
+#endif	/* __ASSEMBLY__ */
+#endif /* _S390_PURGATORY_H_ */