x86: braswell: cherryhill: Update dts for SPI lock down

Intel Braswell FSP requires SPI controller settings to be locked down,
let's do this in the chrryhill.dts and remove previous Kconfig option.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/dts/cherryhill.dts b/arch/x86/dts/cherryhill.dts
index 840a669..41e72f3 100644
--- a/arch/x86/dts/cherryhill.dts
+++ b/arch/x86/dts/cherryhill.dts
@@ -143,6 +143,7 @@
 				#address-cells = <1>;
 				#size-cells = <0>;
 				compatible = "intel,ich9-spi";
+				intel,spi-lock-down;
 
 				spi-flash@0 {
 					#address-cells = <1>;