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/arch/arm/cpu/armv8/fsl-layerscape/Kconfig b/arch/arm/cpu/armv8/fsl-layerscape/Kconfig
index 94ec8d5..ed1c4ee 100644
--- a/arch/arm/cpu/armv8/fsl-layerscape/Kconfig
+++ b/arch/arm/cpu/armv8/fsl-layerscape/Kconfig
@@ -71,6 +71,11 @@
 	default 3 if ARCH_LS2080A
 	default 1
 
+config SECURE_BOOT
+	bool
+	help
+		Enable Freescale Secure Boot feature
+
 config SYS_FSL_IFC_BANK_COUNT
 	int "Maximum banks of Integrated flash controller"
 	depends on ARCH_LS1043A || ARCH_LS1046A || ARCH_LS2080A