armv8: fsl-layerscape: Move SECURE_BOOT to Kconfig

Move from CONFIG_SYS_EXTRA_OPTIONS to Kconfig option.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/configs/ls1043ardb_SECURE_BOOT_defconfig b/configs/ls1043ardb_SECURE_BOOT_defconfig
index 6ee0ad0..4f8c6d4 100644
--- a/configs/ls1043ardb_SECURE_BOOT_defconfig
+++ b/configs/ls1043ardb_SECURE_BOOT_defconfig
@@ -5,7 +5,7 @@
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
-CONFIG_SYS_EXTRA_OPTIONS="SECURE_BOOT"
+CONFIG_SECURE_BOOT=y
 CONFIG_BOOTDELAY=10
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_MMC=y