psu-ng: Wait for inventory manager

The phosphor-psu-monitor application should wait for the inventory
manager service. It more specifically needs to wait until the inventory
manager service has created the object path that the power supplies will
be under. Those are needed by the phosphor-gpio-presence service(s) in
order to create/update power supply objects with an updated Present
property based on the GPIO presence line state.

Remove the unnecessary wait for obmc-mapper.target.

Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
Change-Id: I547ed4ee8f4d6d9ae7e4a7f1becc59d0ebd4ba00
diff --git a/services/phosphor-psu-monitor.service b/services/phosphor-psu-monitor.service
index a973a70..8e369b4 100644
--- a/services/phosphor-psu-monitor.service
+++ b/services/phosphor-psu-monitor.service
@@ -1,9 +1,7 @@
 [Unit]
 Description=Phosphor Power Supply Monitor
-Wants=obmc-mapper.target
-After=obmc-mapper.target
-Wants=mapper-wait@-org-openbmc-control-power0.service
-After=mapper-wait@-org-openbmc-control-power0.service
+Wants=mapper-wait@-xyz-openbmc_project-inventory-system.service
+After=mapper-wait@-xyz-openbmc_project-inventory-system.service
 
 [Service]
 Restart=on-failure