scsi: Add SCSI_LOWLEVEL dependency for SCSI_DEBUG

Since Linux 67951f6380732 ("[SCSI] Fix dependency problems in SCSI drivers"),
SCSI_DEBUG is protected by 'if SCSI_LOWLEVEL && SCSI' conditional, so select
SCSI_LOWLEVEL too.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Bruce Ashfield <bruce.ashfield@gmail.com>
Cc: Mariano López <just.another.mariano@gmail.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>