side-switch: add service to run side-switch function

The side switch check should occur on any host firmware boot so put in
the obmc-host-startmin@.target. Ensure this service does not run when
the BMC is reset while the host is at runtime. Do not want to ever cause
a power down of a running host.

Tested:
- Booted system with running firmware at priority 0 and verified a quick
  return and successful boot.
- Booted system with running firmware at priority 1 and verified system
  was powered off, bmc was rebooted to other image, and system auto
  powered on up to operating system.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I5553ab6fb5ebd58734d1169663ea25ede7f37dd3
diff --git a/side-switch/meson.build b/side-switch/meson.build
index 64ac49e..b13e53c 100644
--- a/side-switch/meson.build
+++ b/side-switch/meson.build
@@ -13,3 +13,11 @@
     install: true,
     install_dir: get_option('bindir')
 )
+
+systemd_system_unit_dir = dependency('systemd').get_variable(
+    pkgconfig: 'systemdsystemunitdir',
+    pkgconfig_define: ['prefix', get_option('prefix')])
+
+install_data(
+        'phosphor-bmc-side-switch.service',
+        install_dir: systemd_system_unit_dir)