BugLink: https://bugs.launchpad.net/bugs/1844245

Include a systemd service to simplify the process of loading intel_sgx
during the boot if the user decides to do so.

Since intel_sgx will only be available in linux-azure, restrict the
new service with ConditionVirtualization=microsoft.
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Acked-by: Andy Whitcroft <andy.whitcroft@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
[ Connor Kuehl: dh_installinit on Xenial does not have the --no-enable
  switch, so I've removed that switch from this patch for Xenial. ]
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>