The Poky layer defines a default journald conf file that allows log files on
the file system to grow to a maximum of 64 MiB. However, this size on some
platforms is impossible to address, so this commit reduces the maximum size for
runtime logs to 4 MiB.
https://onedigi.atlassian.net/browse/DEL-8419
Signed-off-by: Arturo Buzarra <arturo.buzarra@digi.com>