power-on: wait for power on once power is turned on

Currently the op-wait-power-on service is started before power is
actually turned on. Ensure this service does not start until the
obmc-power-on-pre@.target completes.

The bootblock logic prevents the obmc-power-on-pre@.target from
completing when a blocking error or code update is occurring. Without
the fix in this commit, the system will not power on but this service
will fail because it is incorrectly started as a part of the
obmc-power-on-pre@.target.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I5539455374b915c3bdad7de15ca651bd36556a73
diff --git a/recipes-phosphor/chassis/obmc-op-control-power/op-wait-power-on@.service b/recipes-phosphor/chassis/obmc-op-control-power/op-wait-power-on@.service
index bc64595..df83832 100644
--- a/recipes-phosphor/chassis/obmc-op-control-power/op-wait-power-on@.service
+++ b/recipes-phosphor/chassis/obmc-op-control-power/op-wait-power-on@.service
@@ -1,5 +1,7 @@
 [Unit]
 Description=Wait for Power%i to turn on
+Wants=obmc-power-start-pre@%i.target
+After=obmc-power-start-pre@%i.target
 Wants=obmc-power-start@%i.target
 Before=obmc-power-start@%i.target
 Wants=mapper-wait@-org-openbmc-control-power%i.service