x86: cros: Check ROM exists before building vboot

All the x86 devicetree files are built at once, whichever board is
actually being built. If coreboot is the target build, CONFIG_ROM_SIZE
is not defined and samus cannot build Chromium OS verified boot. Add
this condition to avoid errors about CONFIG_ROM_SIZE being missing.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>
Reviewed-by: NJaehoon Chung <jh80.chung@samsung.com>

arch/x86/dts/chromebook_coral.dts

@@ -10,7 +10,7 @@
 /include/ "rtc.dtsi"
 /include/ "tsc_timer.dtsi"
 
-#ifdef CONFIG_CHROMEOS_VBOOT
+#if defined(CONFIG_CHROMEOS_VBOOT) && defined(CONFIG_ROM_SIZE)
 #include "chromeos-x86.dtsi"
 #include "flashmap-x86-ro.dtsi"
 #include "flashmap-16mb-rw.dtsi"

arch/x86/dts/chromebook_samus.dts

@@ -11,7 +11,7 @@
 
 #include "smbios.dtsi"
 
-#ifdef CONFIG_CHROMEOS_VBOOT
+#if defined(CONFIG_CHROMEOS_VBOOT) && defined(CONFIG_ROM_SIZE)
 #include "chromeos-x86.dtsi"
 #include "flashmap-x86-ro.dtsi"
 #include "flashmap-8mb-rw.dtsi"