Split scsi.c

Split scsi.c

Move decoders of SG_IO v3 and v4 APIs into separate files,
compile generic SG_IO decoder unconditionally.

* sg_io_v3.c: New file.
* sg_io_v4.c: Likewise.
* Makefile.am (strace_SOURCES): Add them.
* defs.h (decode_sg_io_v3, decode_sg_io_v4): New prototypes.
* ioctl.c (ioctl_decode): Remove [HAVE_SCSI_SG_H] condition.
* scsi.c: (print_sg_io_res): Remove.
(print_sg_io_req): Rename to decode_sg_io, replace print_sg_io_v3_req
with decode_sg_io_v3, replace print_sg_io_v4_req with decode_sg_io_v4,
compile uncoditionally.
(scsi_ioctl): Replace print_sg_io_req and print_sg_io_res
with decode_sg_io, compile uncoditionally.
Move [HAVE_SCSI_SG_H] code to sg_io_v3.c.
Move [HAVE_LINUX_BSG_H] code to sg_io_v4.c.