systemd: Fix misc journald memory bugs

systemd: Fix misc journald memory bugs

These set of patches fix journald exhibiting some issues
under load.

One of the prevelant issues is that when appending to journal
it is not able to allocate memory and starts taking 100% cpu
spewing errors like

systemd-journald[2934]: Failed to write entry (19 items, 452 bytes), ignoring: Cannot allocate memory

Other memory issues crept up with time e.g.vacuuming

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>