This addresses multiple issues:
* Issue #63: initrd is build fresh each time, so tracked files do not matter.
* Issue #144: build time configuration
* Issue #123: allows us to customize the startup experience
* Issue #122: manual start-xen will go away
* Issue #25: tpmtotp PCRs are updated after reading the secret
* Issue #16: insmod now meaures modules
rename TARGET to BOARD (fix#55)
use .INTERMEDIATE trick to avoid building multiple times (fix#52)
Don't touch build/*/.config if we don't have to (fix#51)
This touches most of the module configurations since the
coreboot build process had to add a few new features.
The Linux kernel could make use of it as well if we need
separate x230/chell/qemu kernels, for instance.
