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.

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index 6d7f1c2..a4f98ce 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,9 @@
      is functioning correctly.
    * Added a script to print build environment info for diagnostic use in test
      scripts, which is also now called by all.sh.
+   * 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().
 
 Bugfix
    * Fix for platform time abstraction to avoid dependency issues where a build