package/gpsd: Fix systemd service installation and paths

package/gpsd: Fix systemd service installation and paths

Fix several issues with systemd service file installation for gpsd:

- systemd support in the gpsd build was defaulting to enabled or not
based on whether the host system had systemd directories present. Set
this explicitly based on whether BR2_INIT_SYSTEMD is set.

- The installed systemd service files referenced paths in /usr/local when
the actual binaries are installed in /usr. Replace /usr/local with /usr
in the installed service files.

- When BR2_PACKAGE_HAS_UDEV was enabled, all of the binaries were
re-installed again, along with the udev rules, as part of the
post-install hooks. This overwrites the service files that were just
fixed up. Since udev-install implies install, we can just call
udev-install.

Signed-off-by: Robert Hancock <hancock@sedsystems.ca>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>