linux-yocto: Add scsi_debug module when ptest is in DISTRO_FEATURES
util-linux ptest requires the scsi_debug module to perform eject/mount
tests. This will conditionally add scsi_debug module when ptest is in
DISTRO_FEATURES.
This doesn't include linux-yocto-tiny because the resulting image will
be too big and do_image would complain about this.
[YOCTO #13301]
Signed-off-by: Mariano López <just.another.mariano@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
