Add mISDN core files

drivers/isdn/mISDN/Kconfig

drivers/isdn/mISDN/Makefile

drivers/isdn/mISDN/core.c

drivers/isdn/mISDN/core.h

drivers/isdn/mISDN/fsm.c

drivers/isdn/mISDN/fsm.h

drivers/isdn/mISDN/hwchannel.c

drivers/isdn/mISDN/layer1.c

drivers/isdn/mISDN/layer1.h

drivers/isdn/mISDN/layer2.c

drivers/isdn/mISDN/layer2.h

drivers/isdn/mISDN/socket.c

drivers/isdn/mISDN/stack.c

drivers/isdn/mISDN/tei.c

drivers/isdn/mISDN/timerdev.c

include/linux/mISDNhw.h

include/linux/mISDNif.h