dm: scsi: Add a migration deadline for scsi

Very few boards remain to be migrated:

   am57xx_hs_evm_usb
   controlcenterdc
   highbank
   ls1021atsn_qspi
   ls1021atsn_sdcard
   ls1021atwr_sdcard_ifc_SECURE_BOOT
   ls1046ardb_sdcard_SECURE_BOOT
   ls1088ardb_sdcard_qspi_SECURE_BOOT
   omap5_uevm
   pg_wcom_expu1
   pg_wcom_seli8
   sandbox
   sandbox64
   sandbox_flattree
   sandbox_noinst
   sandbox_spl
   tools-only

Addd a migration deadline for a year out.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>