package/gpsd: do not interact with systemd on install

When building on a systemd-based host for a systemd-based target, gpsd's
buildsystem will try to tell systemd to reload the its configuration and
recreate the entire dependency tree of services.

Of course, this can not work when run as a user:
    >>> gpsd 3.16 Installing to target
    ==== AUTHENTICATING FOR org.freedesktop.systemd1.reload-daemon ===
    Authentication is required to reload the systemd state.
    Authenticating as: root
    Password:

In fact, this does not even mean anything in cross-compilation.

Fortunately, upstream has already fixed their sin, so we backport it
(tweaked to apply onto 3.16).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>