package/freerdp: optional systemd's journald support

FreeRDP now has support for writing to the journal, so we must ensure
proper dependency and correct options.

Partially fixes:
    http://autobuild.buildroot.org/results/81aa66ddd88919295ccb5f34b527b737627263a7/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>