common: Add a new lz4.h header file

Add a header file to house the lz4 compression function. Add a comment
while we are here, since it not even clear from the name what the function
actuall does.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/lz4.h

@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2019 Google LLC
+ */
+
+#ifndef __LZ4_H
+#define __LZ4_H
+
+/**
+ * ulz4fn() - Decompress LZ4 data
+ *
+ * @src: Source data to decompress
+ * @srcn: Length of source data
+ * @dst: Destination for uncompressed data
+ * @dstn: Returns length of uncompressed data
+ * @return 0 if OK, -EPROTONOSUPPORT if the magic number or version number are
+ *	not recognised or independent blocks are used, -EINVAL if the reserved
+ *	fields are non-zero, or input is overrun, -EENOBUFS if the destination
+ *	buffer is overrun, -EEPROTO if the compressed data causes an error in
+ *	the decompression algorithm
+ */
+int ulz4fn(const void *src, size_t srcn, void *dst, size_t *dstn);
+
+#endif