systemd: add input group

It's used by 50-default-udev.rules for input-class devices.

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

package/systemd/systemd.mk

@@ -179,6 +179,7 @@ define SYSTEMD_USERS
 	systemd-bus-proxy -1 systemd-bus-proxy -1 * - - - Proxy D-Bus messages to/from a bus
 	systemd-timesync -1 systemd-timesync -1 * - - - Network Time Synchronization
 	systemd-network -1 systemd-network -1 * - - - Network Manager
+	- - input -1 * - - - Input device group
 endef
 
 define SYSTEMD_DISABLE_SERVICE_TTY1