Add driver for multi-subchannel devices (ctc and lcs)

The cu3088 driver is an metadriver to make the ctc and lcs
(potentially also claw) drivers work with the new
channel subsystem driver. It uses the ccwgroup driver to
group subchannels for ctc and lcs.

Authors:
	Arnd Bergmann <arndb@de.ibm.com>
	Cornelia Huck <cohuck@de.ibm.com>