armv8: layerscape: Drop u-boot-with-spl.bin for selected boards

For SPL boot with PBL, u-boot-with-spl-pbl.bin is the final image.
Drop unused u-boot-with-spl.bin.

Signed-off-by: York Sun <york.sun@nxp.com>
CC: Mingkai Hu <mingkai.hu@nxp.com>
CC: Ruchika Gupta <ruchika.gupta@nxp.com>
CC: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
CC: Udit Agarwal <udit.agarwal@nxp.com>
CC: Sumit Garg <sumit.garg@nxp.com>
CC: Priyanka Jain <priyanka.jain@nxp.com>