Issue found during installing systemd unit from repo

[Lei YU]

This email is to introduce an issue found by George Liu that the
systemd unit variables are not correctly replaced by the value when
installing from the repo.

For details please refer to https://github.com/openbmc/openbmc/issues/3627

The question here is, should we fix the systemd units themselves in
the repo, or should we try to figure out how to install the services
*correctly* in bitbake?

Be noted that the issue impacts the below service for
meta-witherspoon, but it's not clear if there are other services
impacted for other machines.
* phosphor-gpio-monitor at .service
* phosphor-gpio-presence at .service
* power-supply-monitor at .service

@Brad Bishop your inputs are appreciated.

Thanks!