Split utils function from main

src/utils.h

@@ -0,0 +1,23 @@
+/*******************************************************************************
+*   Ledger Ethereum App
+*   (c) 2016-2019 Ledger
+*
+*  Licensed 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.
+********************************************************************************/
+
+#ifndef _UTILS_H_
+#define _UTILS_H_
+
+void array_hexstr(char *strbuf, const void *bin, unsigned int len);
+
+#endif /* _UTILS_H_ */