Install example psu-update@.service

The repo needs an example psu-update@.service, it was expected to be
installed by a bitbake recipe, but during the recipe review it turns
out that the repo is better to install a default one and it could be
overriden by a bbappend.

Move the psu-update@.service from vendor-example to services directory
and install it.

Tested: Verify the service is installed.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: I105b201972b32ca3d9e14878b92c9d038a41cbdb
diff --git a/services/psu-update@.service b/services/psu-update@.service
new file mode 100644
index 0000000..08e3c6e
--- /dev/null
+++ b/services/psu-update@.service
@@ -0,0 +1,17 @@
+# This service shall be started with two arguments:
+#  * The PSU inventory DBus object
+#  * The path of the PSU images
+# E.g.
+#  "psu-update@-xyz-openbmc_project-inventory-system-chassis-motherboard-powersupply0\x20-tmp-image-abcdefg.service"
+# expands to
+#  /bin/echo To update /xyz/openbmc_project/inventory/system/chassis/motherboard/powersupply0 /tmp/image/abcdefg
+
+[Unit]
+Description=Update PSU %I
+
+[Service]
+Type=oneshot
+RemainAfterExit=no
+Environment="ARGS=%I"
+ExecStart=/bin/echo To update $ARGS
+ExecStart=/bin/false