x86: link: Add PCH driver to support SPI Flash

U-Boot on coreboot does not have a driver for the PCH so cannot see the
SPI peripheral now that it has moved inside the PCH. Add a simple driver so
that SPI flash works again.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/dts/chromebook_link.dts b/arch/x86/dts/chromebook_link.dts
index b450c3c..7c7034c 100644
--- a/arch/x86/dts/chromebook_link.dts
+++ b/arch/x86/dts/chromebook_link.dts
@@ -181,7 +181,7 @@
 
 		pch {
 			reg = <0x0000f800 0 0 0 0>;
-			compatible = "intel,bd82x6x";
+			compatible = "intel,bd82x6x", "intel,pch";
 			u-boot,dm-pre-reloc;
 			#address-cells = <1>;
 			#size-cells = <1>;