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

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>