mISDN: Add XHFC support for embedded Speech-Design board to hfcmulti

New version without emulating arch specific stuff for the other
architectures, the special IO and init functions for the 8xx
microcontroller are in a separate include file.

Signed-off-by: Andreas Eversberg <andreas@eversberg.eu>
Signed-off-by: Karsten Keil <keil@b1-systems.de>
Signed-off-by: David S. Miller <davem@davemloft.net>