s390/qdio: split do_QDIO()

The callers know what type of queue they want to work with. Introduce
type-specific variants to add buffers on an {Input,Output} queue, so
that we can avoid some function parameters and the de-muxing into
type-specific hot paths.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>