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/test/lib/Makefile b/test/lib/Makefile
index aa2e66b..6fd0514 100644
--- a/test/lib/Makefile
+++ b/test/lib/Makefile
@@ -17,3 +17,4 @@
 obj-$(CONFIG_UT_LIB_RSA) += rsa.o
 obj-$(CONFIG_AES) += test_aes.o
 obj-$(CONFIG_GETOPT) += getopt.o
+obj-$(CONFIG_UT_LIB_CRYPT) += test_crypt.o