lib: add crypt subsystem

Add the basic functionality required to support the standard crypt
format.
The files crypt-sha256.c and crypt-sha512.c originate from libxcrypt and
their formatting is therefor retained.
The integration is done via a crypt_compare() function in crypt.c.

```
libxcrypt $ git describe --long --always --all
tags/v4.4.17-0-g6b110bc
```

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/lib/crypt/alg-sha512.h b/lib/crypt/alg-sha512.h
new file mode 100644
index 0000000..93b6109
--- /dev/null
+++ b/lib/crypt/alg-sha512.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/* Copyright (C) 2020 Steffen Jaeckel <jaeckel-floss@eyet-services.de> */
+
+#ifndef USE_HOSTCC
+#include "common.h"
+#else
+#include <string.h>
+#endif
+
+#include "u-boot/sha512.h"
+
+#define INCLUDE_sha512crypt 1
+
+#define SHA512_CTX sha512_context
+#define SHA512_Init sha512_starts
+#define SHA512_Update(c, i, l) sha512_update(c, (const void *)i, l)
+#define SHA512_Final(b, c) sha512_finish(c, b)