Exclude NO_SHA224 option from scripts/config.pl

As a negative option that removes a feature it should be excluded.
diff --git a/scripts/config.pl b/scripts/config.pl
index 751ea1d..e18df92 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -30,6 +30,7 @@
 #   MBEDTLS_NO_PLATFORM_ENTROPY
 #   MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 #   MBEDTLS_REMOVE_3DES_CIPHERSUITES
+#   MBEDTLS_SHA256_NO_SHA224
 #   MBEDTLS_SSL_HW_RECORD_ACCEL
 #   MBEDTLS_SSL_PROTO_NO_DTLS
 #   MBEDTLS_SSL_NO_SESSION_CACHE
@@ -99,6 +100,7 @@
 MBEDTLS_RSA_NO_CRT
 MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 MBEDTLS_REMOVE_3DES_CIPHERSUITES
+MBEDTLS_SHA256_NO_SHA224
 MBEDTLS_SSL_HW_RECORD_ACCEL
 MBEDTLS_SSL_PROTO_NO_TLS
 MBEDTLS_SSL_NO_SESSION_CACHE