entity-manager: systemd: use dbus instead of simple

Use systemd service type dbus instead of simple.  This avoids entity
manager client applications that have correctly ordered themselves after
entity manager from attempting to connect before it has claimed a bus
name.

When Type=dbus, systemd automatically adds an implicit dependency on
dbus.socket (so remove the unnecessary dependency on dbus.service).

Tested: systemctl restart xyz.openbmc_project.EntityManager works
Change-Id: I450b4ce28d87dfad9143b8b20cd9445e00dd07b0
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/service_files/xyz.openbmc_project.EntityManager.service b/service_files/xyz.openbmc_project.EntityManager.service
index 651b0f2..448e61d 100644
--- a/service_files/xyz.openbmc_project.EntityManager.service
+++ b/service_files/xyz.openbmc_project.EntityManager.service
@@ -1,13 +1,13 @@
 [Unit]
 Description=Entity Manager
-After=dbus.service
 
 [Service]
 ExecStartPre=/bin/mkdir -p /var/configuration
 ExecStartPre=/bin/mkdir -p /tmp/overlays
 ExecStart=/usr/bin/entity-manager
 Restart=always
-Type=simple
+Type=dbus
+BusName=xyz.openbmc_project.EntityManager
 
 [Install]
 WantedBy=basic.target