x86: coreboot: Move coreboot-specific defines from coreboot.h to Kconfig

There are many places in the U-Boot source tree which refer to
CONFIG_SYS_COREBOOT, CONFIG_CBMEM_CONSOLE and CONFIG_VIDEO_COREBOOT
that is currently defined in coreboot.h.

Move them to arch/x86/cpu/coreboot/Kconfig so that we can switch
to board configuration file to build U-Boot later.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 512b6f6..90e828a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -344,6 +344,8 @@
 	help
 	  The running frequency in MHz of Time-Stamp Counter (TSC).
 
+source "arch/x86/cpu/coreboot/Kconfig"
+
 source "arch/x86/cpu/ivybridge/Kconfig"
 
 source "arch/x86/cpu/queensbay/Kconfig"