gigaset: allow building without I4L

Add a dummy LL interface to the Gigaset driver so that it can be
built and, in a limited way, used without the ISDN4Linux subsystem.

Impact: new configuration alternative
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/isdn/gigaset/Makefile b/drivers/isdn/gigaset/Makefile
index e9d3189..d429202 100644
--- a/drivers/isdn/gigaset/Makefile
+++ b/drivers/isdn/gigaset/Makefile
@@ -1,4 +1,6 @@
-gigaset-y := common.o interface.o proc.o ev-layer.o i4l.o asyncdata.o
+gigaset-y := common.o interface.o proc.o ev-layer.o asyncdata.o
+gigaset-$(CONFIG_GIGASET_I4L) += i4l.o
+gigaset-$(CONFIG_GIGASET_DUMMYLL) += dummyll.o
 usb_gigaset-y := usb-gigaset.o
 ser_gigaset-y := ser-gigaset.o
 bas_gigaset-y := bas-gigaset.o isocdata.o