[SCSI] zfcp: Introduce header file for qdio structs and inline functions

Move the qdio related structs and some helper functions to a new
zfcp_qdio.h header file. While doing this, rename the struct
zfcp_queue_req to zfcp_qdio_req to adhere to the naming scheme used in
zfcp. This allows a better seperation of the qdio code and inlining
the helper functions will save some function calls.

Reviewed-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>