x86: Rename coreboot.dsti to serial.dtsi

The name of coreboot.dtsi is misleading, as it actually describes
the legacy serial port device node.

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

arch/x86/dts/crownbay.dts

@@ -6,7 +6,7 @@
 
 /dts-v1/;
 
-/include/ "coreboot.dtsi"
+/include/ "serial.dtsi"
 
 / {
 	#address-cells = <1>;

arch/x86/dts/link.dts

@@ -1,6 +1,6 @@
 /dts-v1/;
 
-/include/ "coreboot.dtsi"
+/include/ "serial.dtsi"
 
 / {
 	#address-cells = <1>;