- Fix typo in sparc_v9 code, in ns87415, just introduced.

 - Eliminate unnecessary struct hd_drive_hob_hdr those are
   in reality precisely the same registers as usual.

 - Eliminate control_t, nowhere used type.

 - Unfold ide_init_drive_cmd() at the places where it's used. This makes obvious
   that REQ_DRIVE_CMD gets only used on the ioctl command path.