[SCSI] zfcp: Move DBF definitions to private header file

Unclutter the global zfcp_def.h header. Move everything required to
call into the debug feature to a new header file.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Martin Peschke <mp3@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>