Allow the entry_name size to be set in config.h

Allow the size of the entry_name character array in x509_crt.c to be
configurable through a macro in config.h. entry_name holds a
path/filename string. The macro introduced in
MBEDTLS_X509_MAX_FILE_PATH_LEN.
diff --git a/ChangeLog b/ChangeLog
index 2007c41..662ed8f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -44,6 +44,9 @@
      buffer.
    * Fix invalid buffer sizes passed to zlib during record compression and
      decompression.
+   * Added the macro MBEDTLS_X509_MAX_FILE_PATH_LEN that enables the user to
+     configure the maximum length of a file path that can be buffered when
+     calling mbedtls_x509_crt_parse_path().
 
 Changes
    * Improve testing in configurations that omit certain hashes or