armv8: fsl-layerscape: Fix SECURE_BOOT config

Without a prompt in Kconfig, SECURE_BOOT cannot be selected by
defconfig. The option was dropped unintentionally when defconfig
files were cleaned up. Three targets were impacted
ls1043ardb_SECURE_BOOT, ls2080ardb_SECURE_BOOT,
ls2080aqds_SECURE_BOOT.

Signed-off-by: York Sun <york.sun@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
4 files changed