U-Boot runtime configuration is done with a device-tree file, which is
built alongside the executable in the upstream build system, and must be
available to U-Boot at runtime.

This device-tree is normally not linked into the default "u-boot" ELF
file. So far we have been handling it by re-creating a "u-boot.elf" from
the raw binary parts by setting REMAKE_ELF, and using that as the
coreboot payload. Unfortunately, that fails to build for x86 boards,
more specificly the "coreboot" boards upstream.

It's also possible (but discouraged) to set OF_EMBED to embed the
device-tree file into the U-Boot itself, in which case we could use the
"u-boot" file as the payload on the "coreboot" boards. Add support for
using the "u-boot" file as the payload if "u-boot.elf" doesn't exist.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

The roms_helper script skips building crossgcc-i386 if its target
directory exists. Skip it for other architectures as well.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

Add the coreboot-built cross-architecture toolchains to the PATH so that
modules and payloads can use them. When building for a foreign-arch
board, also export CROSS_COMPILE pointing to the appropriate prefix.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

This re-applies commit a69855f7e448 ("Build 32-bit crossgcc for AArch64
as well") which was inexplicably reverted along with unrelated changes.
Mention in a comment that building crossgcc-arm is necessary for
AArch64.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

When overriding which payloads will be built with the -p command line
argument, the roms_helper script builds the Memtest86+ payload before
checking if it should be disabled. Move the build command after the
command line override.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

When overriding which payloads will be built with the -p command line
argument, the roms_helper script doesn't disable the U-Boot payload.
Disable it in this case.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

the --nuke option in ifdtool will be used instead, to nuke
the ME regions in specific rom sets (and cbfstool will be
used to delete mrc.bin files from rom sets)

the new method being implemented is heavier on disk io, but
simplifies lbmk, and disk io could still be optimised in
the following ways:

* when copying roms from boards with ME in them, use
  ifdtool --nuke to get filename.rom.new, and *move* (not copy)
  filename.rom.new to the new destination (for use with tar)

* possibly modify ifdtool to make efficient use of mmap for
  disk i/o; it currently loads entire roms into an allocated
  buffer in memory