[S390] cio: move asms to generic header

The ssch and csch functions are not I/O subchannel specific,
thus move them from io_sch.h to ioasm.h

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>