Enable cgroups in Linux if we use systemd

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

linux/linux.mk

@@ -162,6 +162,8 @@ define LINUX_CONFIGURE_CMDS
 		$(call KCONFIG_ENABLE_OPT,CONFIG_DEVTMPFS_MOUNT,$(@D)/.config))
 	$(if $(BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV),
 		$(call KCONFIG_SET_OPT,CONFIG_UEVENT_HELPER_PATH,\"/sbin/mdev\",$(@D)/.config))
+	$(if $(BR2_PACKAGE_SYSTEMD),
+		$(call KCONFIG_ENABLE_OPT,CONFIG_CGROUPS,$(@D)/.config))
 	yes '' | $(TARGET_MAKE_ENV) $(MAKE1) $(LINUX_MAKE_FLAGS) -C $(@D) oldconfig
 endef