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/Makefile b/lib/Makefile
index d8055d3..5cd0c9c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -65,6 +65,7 @@
 obj-$(CONFIG_SHA1) += sha1.o
 obj-$(CONFIG_SHA256) += sha256.o
 obj-$(CONFIG_SHA512_ALGO) += sha512.o
+obj-$(CONFIG_CRYPT_PW) += crypt/
 
 obj-$(CONFIG_$(SPL_)ZLIB) += zlib/
 obj-$(CONFIG_$(SPL_)ZSTD) += zstd/