systemd: enable create-log-dirs

systemd: enable create-log-dirs

By default, create-log-dirs  is enabled in systemd, and a link
/var/log/README will be created, point to {{DOC_DIR}}/README.logs, but,
for oe, there are two problems here, firstly, DOC_DIR is packaged in
another package systemd-doc, so /var/log/README is a dead link when
systemd-doc is not installed, secondly, even systemd-doc is installed,
when volatile log is used, DOC_DIR is a wrong relateive path, Refer [1].

So in commit [2], we disable create-log-dirs for above issue. with this
change, /var/log/journal is not created, and /run/log is used, this
makes systemd log always non persistent, refer [3][4]. if user need
persistent log, they need to disable volatile log, and also  change
journald.conf, make "Storage" to "persistent". This is a behavoir change.
Previously, to make systemd log persistent, user only need to disable
volatile log.

This commit reenable create-log-dirs to revert the behavior change, and
since README is not very userful, just remove it.

[ YOCTO #15678 ]

[1] https://github.com/systemd/systemd/blob/main/tmpfiles.d/legacy.conf.in#L16
[2] https://git.openembedded.org/openembedded-core/commit/?id=18d46e11d85da1f6feaba5a135931e43060024d6
[3] https://github.com/systemd/systemd/blob/main/src/journal/meson.build#L189
[4] https://www.freedesktop.org/software/systemd/man/journald.conf.html
[5] https://bugzilla.yoctoproject.org/show_bug.cgi?id=15678

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>