payloads/U-Boot: Tidy up the U-Boot build

This doesn't work at present, merely printing an error when U-Boot is
selected as a payload. This is because it adds a file into the U-Boot
tree which makes U-Boot's build system think that the tree is unclean.

Update the rules to put the tag file outside the source tree. Use an
out-of-tree build for U-Boot to avoid changing the source tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
Change-Id: I24d6545b54f97afeefaca3ffed79eec2e7afacb4
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59600
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

0 files changed, 0 insertions, 0 deletions