platform/mtpd: Add systemd service file

systemd unit file that starts the mtpd daemon
BUG=chromium:583671
TEST=Checked that the mtpd daemon is up and running with
  "systemctl status mtpd". Plugged phone and I could browse
  files.
CQ-DEPEND=CL:351980
Change-Id: I2b9286ca3f6915ecf8e596f8f8fef27d850725e5
Reviewed-on: https://chromium-review.googlesource.com/351970
Commit-Ready: Sabin Floares <sabin.floares@intel.com>
Tested-by: Sabin Floares <sabin.floares@intel.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/mtpd.service b/mtpd.service
new file mode 100644
index 0000000..9335818
--- /dev/null
+++ b/mtpd.service
@@ -0,0 +1,14 @@
+# Copyright 2016 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+[Unit]
+Description=Media Transfer Protocol Daemon
+PartOf=system-services.target
+After=system-services.target
+[Service]
+Restart=always
+Environment="MTPD_MINLOGLEVEL=1"
+ExecStart=/sbin/minijail0 -u mtp -g mtp -G -n -S \
+	/opt/google/mtpd/mtpd-seccomp.policy -- \
+	/opt/google/mtpd/mtpd -minloglevel="${MTPD_MINLOGLEVEL}"