systemd: set cgroupv2 PACKAGECONFIG

Enable the cgroupv2 feature flag which should disable some legacy
code around cgroup handling that we do not need due to running
newer kernels.

Change-Id: I487b71ba2b81ea2ff54280072220e65c95c4caab
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meta-phosphor/recipes-core/systemd/systemd_%.bbappend b/meta-phosphor/recipes-core/systemd/systemd_%.bbappend
index bfe318a..847d324 100644
--- a/meta-phosphor/recipes-core/systemd/systemd_%.bbappend
+++ b/meta-phosphor/recipes-core/systemd/systemd_%.bbappend
@@ -1,5 +1,6 @@
 FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"
 PACKAGECONFIG = "\
+        cgroupv2 \
         coredump \
         hostnamed \
         networkd \