x86: Make chromebook_link the default board for coreboot

Change SYS_CONFIG_NAME and DEFAULT_DEVICE_TREE to chromebook_link
which is currently the only real board officially supported to run
U-Boot loaded by coreboot.

Note the symbolic link file chromebook_link.dts is deleted and
link.dts is renamed to chromebook_link.dts.

To avoid multiple definition of video_hw_init, the CONFIG_VIDEO_X86
define needs to be moved to arch/x86/cpu/ivybridge/Kconfig.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index e69de29..fdbf3f6 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -0,0 +1,8 @@
+config VIDEO_X86
+	bool "Enable x86 video driver support"
+	depends on X86
+	default n
+	help
+	  Turn on this option to enable a very simple driver which uses vesa
+	  to discover the video mode and then provides a frame buffer for use
+	  by U-Boot.