don't put multiple downloads in the same files, except
when they are dependencies that go inside the directory
of another download.

by doing this, the following functionality will become
possible: clean every project or build every project,
or maybe fetch every project, based entirely on the
names of these files.

this will be used later to simplify the release script.

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

build/release/src was partly re-written to accomodate this

memtest86plus was patched to have a central Makefile, and
lbmk modified to use that, rather than mess with build32
and build64. the central Makefile just builds both targets
or cleans both targets

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

With this change, it's still possible to have a single
file at config/git/revisions, but this has been scrapped.

Instead, multiple files now exist under config/git/ with
the same modules declared, but the files are separated
logically. List of files under config/git:

* bios_extract
* biosutilities
* coreboot
* flashrom
* grub (gnulib also defined here)
* me_cleaner
* memtest86plus
* seabios
* serprog (multiple projects defined)
* u-boot
* uefitool

The rationale behind this change is simple: in the future,
we will stop relying on build systems within imported
projects for the import of git submodules. Instead, we
will handle them directly in lbmk.

Additionally, a Linux payload is planned for Libreboot, made
easier by the recent audit (script handle/make/config makes
it easy to integrate Linux, and handle cross-compilers for
userland utilities); a "linux" file under config/git/ could
also define rules for each project besides linux, such as
musl libc, busybox and other utilities.

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