Add Mynewt support for bundled tinycrypt + mbedtls

This commit removes the pseudo tinycrypt package based on symlinks
by adding a new pkg.yml to ext/tinycrypt and using it directly. It
also uses the new mbed-tls bundled ASN1 parser when EC256 is selected.

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/ext/tinycrypt/lib/pkg.yml b/ext/tinycrypt/lib/pkg.yml
new file mode 100644
index 0000000..42db8aa
--- /dev/null
+++ b/ext/tinycrypt/lib/pkg.yml
@@ -0,0 +1,30 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+# 
+#  http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+
+pkg.name: ext/tinycrypt/lib
+pkg.description: "MCUboot's bundled tinycrypt"
+pkg.author: "Apache Mynewt <dev@mynewt.apache.org>"
+pkg.homepage: "http://mynewt.apache.org/"
+pkg.keywords:
+
+pkg.src_dirs:
+  - "source"
+
+pkg.cflags:
+    - "-std=c99"