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/configs/chromebook_link_defconfig b/configs/chromebook_link_defconfig
index b83803e..e956835 100644
--- a/configs/chromebook_link_defconfig
+++ b/configs/chromebook_link_defconfig
@@ -6,5 +6,6 @@
 CONFIG_DEFAULT_DEVICE_TREE="chromebook_link"
 CONFIG_HAVE_MRC=y
 CONFIG_SMM_TSEG_SIZE=0x800000
+CONFIG_VIDEO_X86=y
 CONFIG_FRAMEBUFFER_SET_VESA_MODE=y
 CONFIG_FRAMEBUFFER_VESA_MODE_11A=y