aes: Add AES-XTS cipher block mode

Add XEX-based tweaked-codebook mode with ciphertext stealing (XTS) for
use with AES.
diff --git a/library/version_features.c b/library/version_features.c
index a452caf..861276a 100644
--- a/library/version_features.c
+++ b/library/version_features.c
@@ -252,6 +252,9 @@
 #if defined(MBEDTLS_CIPHER_MODE_CTR)
     "MBEDTLS_CIPHER_MODE_CTR",
 #endif /* MBEDTLS_CIPHER_MODE_CTR */
+#if defined(MBEDTLS_CIPHER_MODE_XTS)
+    "MBEDTLS_CIPHER_MODE_XTS",
+#endif /* MBEDTLS_CIPHER_MODE_XTS */
 #if defined(MBEDTLS_CIPHER_NULL_CIPHER)
     "MBEDTLS_CIPHER_NULL_CIPHER",
 #endif /* MBEDTLS_CIPHER_NULL_CIPHER */