meta-tizen: set Tizen's systemd_unitdir

meta-tizen: set Tizen's systemd_unitdir

Tizen uses a different path for systemd unit files than Yocto. After
setting it in tizen.conf, it's no longer necesssary to list the unit
files in alsa-utils.

However, the default packaging of alsa-utils puts them into
alsa-utils-alsactl, which may or may not be a problem for Tizen.

Change-Id: I52f85329b04110bc7658a1f543bd6e72615e586c
(From meta-tizen rev: 83a99f95b1a316453f50c94c02811ac1f77cc793)

Signed-off-by: Ronan Le Martret <ronan@fridu.net>
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>