Payload infrastructure

by Cai Bai Yin for coreboot

coreboot now use kconfig to build the whole project.But the libpayload is not included in the kconfig tree. The main job of this project is adding payload build support to the coreboot kconfig and crossgcc build which would make the project as an whole by the kconfig.After that there is no need to build coreboot and payload alone. my additional work may including 1)generate an Bill of Materials (BoM) for the build. 2)add readline support for filo, which would make the interface more humanize.