ide: remove ->supports_dsc_overlap field from ide_driver_t

* Use drive->media and drive->scsi to check if ->dsc_overlap
  can be set by HDIO_SET_NICE ioctl in generic_ide_ioctl().

* Remove unused ->supports_dsc_overlap field from ide_driver_t.

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>