powerpc: mpc85xx: 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/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 1d2e027..f782695 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -435,6 +435,12 @@
 config ARCH_T4240
 	bool
 
+config SECURE_BOOT
+	bool	"Secure Boot"
+	help
+		Enable Freescale Secure Boot feature. Normally selected
+		by defconfig. If unsure, do not change.
+
 config MAX_CPUS
 	int "Maximum number of CPUs permitted for MPC85xx"
 	default 12 if ARCH_T4240