x86: cougarcanyon2: Update dts for SPI lock down

It turns out that like Braswell, Intel FSP for IvyBridge requires
SPI controller settings to be locked down, as the U-Boot ICH SPI
driver fails with the following message on Cougar Canyon 2 board:

  "ICH SPI: Opcode 9f not found"

Update the SPI node property to indicate this fact.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/x86/dts/cougarcanyon2.dts

@@ -70,6 +70,8 @@
 				#address-cells = <1>;
 				#size-cells = <0>;
 				compatible = "intel,ich9-spi";
+				intel,spi-lock-down;
+
 				spi-flash@0 {
 					reg = <0>;
 					compatible = "winbond,w25q64bv", "spi-flash";