data: make service dbus-activatable

Always install the dbus service file and specify the systemd
unit file in it. This makes the service dbus-activatable and
thus we don't need to explicitly enable it (also we have one
less daemon running, if it is not needed).

data/com.feralinteractive.GameMode.service.in

@@ -1,3 +1,4 @@
 [D-BUS Service]
 Name=com.feralinteractive.GameMode
 Exec=@BINDIR@/gamemoded -d
+SystemdService=gamemoded.service

data/meson.build

@@ -10,7 +10,8 @@ if with_systemd == true
         configuration: data_conf,
         install_dir: path_systemd_unit_dir,
     )
-else
+endif
+
 # Install the D-BUS service file
 configure_file(
   input: 'com.feralinteractive.GameMode.service.in',
@@ -18,7 +19,7 @@ else
   configuration: data_conf,
   install_dir: path_dbus_service_dir,
 )
-endif
+
 
 # Install the Polkit action file in all cases
 configure_file(

meson.build

@@ -53,13 +53,13 @@ if with_systemd == true
         pkgconfig_systemd = dependency('systemd')
         path_systemd_unit_dir = pkgconfig_systemd.get_pkgconfig_variable('systemduserunitdir')
     endif
-else
+endif
+
 # Set the dbus path as appropriate.
 path_dbus_service_dir = get_option('with-dbus-service-dir')
 if path_dbus_service_dir == ''
   path_dbus_service_dir = join_paths(path_datadir, 'dbus-1', 'services')
 endif
-endif
 
 path_polkit_action_dir = join_paths(path_datadir, 'polkit-1', 'actions')
 
@@ -114,11 +114,10 @@ if with_systemd == true
 report += [
     '    systemd user unit directory:            @0@'.format(path_systemd_unit_dir),
 ]
-else
+endif
 report += [
     '    D-BUS service directory:                @0@'.format(path_dbus_service_dir),
 ]
-endif
 
 report += [