usb_gigaset: suspend support

Add basic suspend/resume support to the usb_gigaset driver for the Siemens
Gigaset M105 USB DECT adapter.

Only the USB aspects are handled so far; the ISDN subsystem is not notified in
any way, for lack of information about how to do that.  The driver does not
check for active connections before suspending.  They will be dropped when the
device loses USB power.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Cc: Greg KH <gregkh@suse.de>
Cc: Hansjoerg Lipp <hjlipp@web.de>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>