systemd-units: ensure required class is inherited

Although the project is trying to get away from the use of
obmc-phosphor-systemd, need to ensure it's being used where required.
This recipe utilizes it to create chassis/host synchronization and
action targets.

(From meta-phosphor rev: de30c9857a4b93e657a8c32af33f3c84f659463c)

Change-Id: I7ddc13c2997f8a38a59e81250aa1b03a76f7625c
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/meta-phosphor/recipes-phosphor/state/phosphor-state-manager_git.bb b/meta-phosphor/recipes-phosphor/state/phosphor-state-manager_git.bb
index a73f387..5d2357e 100644
--- a/meta-phosphor/recipes-phosphor/state/phosphor-state-manager_git.bb
+++ b/meta-phosphor/recipes-phosphor/state/phosphor-state-manager_git.bb
@@ -44,6 +44,7 @@
 
 inherit meson pkgconfig
 inherit obmc-phosphor-dbus-service
+inherit obmc-phosphor-systemd
 
 DEPENDS += "sdbusplus"
 DEPENDS += "sdeventplus"