witherspoon: Use systemd_unitdir

Somewhere between systemd 234 and 237 the install process stopped making
/usr/lib/systemd/network for us.  When we move to Yocto 2.5 this will
result in an install failure.

bitbake.conf provides a variable for /lib/systemd.  Use it, as it's the
correct location for these configuration/unit files anyhow.

Tested: Booted QEMU witherspoon image to shell:
Change-Id: I000b6f1b5548efb920d31226558159cba3deb8d6
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-core/systemd_%.bbappend b/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-core/systemd_%.bbappend
index b4bfc1f..847714b 100644
--- a/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-core/systemd_%.bbappend
+++ b/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-core/systemd_%.bbappend
@@ -3,12 +3,12 @@
 SRC_URI += "file://systemd-journald-override.conf"
 SRC_URI += "file://journald-size-policy.conf"
 
-FILES_${PN} += "${libdir}/systemd/journald.conf.d/journald-storage-policy.conf"
+FILES_${PN} += "${systemd_unitdir}/journald.conf.d/journald-storage-policy.conf"
 FILES_${PN} += "${systemd_system_unitdir}/systemd-journald.service.d/systemd-journald-override.conf"
-FILES_${PN} += "${libdir}/systemd/journald.conf.d/journald-size-policy.conf"
+FILES_${PN} += "${systemd_unitdir}/journald.conf.d/journald-size-policy.conf"
 
 do_install_append() {
-        install -m 644 -D ${WORKDIR}/journald-storage-policy.conf ${D}${libdir}/systemd/journald.conf.d/journald-storage-policy.conf
+        install -m 644 -D ${WORKDIR}/journald-storage-policy.conf ${D}${systemd_unitdir}/journald.conf.d/journald-storage-policy.conf
         install -m 644 -D ${WORKDIR}/systemd-journald-override.conf ${D}${systemd_system_unitdir}/systemd-journald.service.d/systemd-journald-override.conf
-        install -m 644 -D ${WORKDIR}/journald-size-policy.conf ${D}${libdir}/systemd/journald.conf.d/journald-size-policy.conf
+        install -m 644 -D ${WORKDIR}/journald-size-policy.conf ${D}${systemd_unitdir}/journald.conf.d/journald-size-policy.conf
 }