certain code checks for build.list, to skip it, for
example in items()

we already use config/data/grub to store grub config data
that applied to all trees

create these directories too:

config/data/coreboot
config/data/u-boot
config/data/seabios

move the respective build.list files in here, and also
to config/data/grub

now multi-tree projects contain, per directory, just the
target.cfg file and the patches directory. this is much
cleaner, because some of the logic can be simplified more

Signed-off-by: Leah Rowe <leah@libreboot.org>