fit: Don't allow verification of images with @ nodes

fit: Don't allow verification of images with @ nodes

When searching for a node called 'fred', any unit address appended to the
name is ignored by libfdt, meaning that 'fred' can match 'fred@1'. This
means that we cannot be sure that the node originally intended is the one
that is used.

Disallow use of nodes with unit addresses.

Update the forge test also, since it uses @ addresses.

CVE-2021-27138

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Bruce Monroe <bruce.monroe@intel.com>
Reported-by: Arie Haenel <arie.haenel@intel.com>
Reported-by: Julien Lenoir <julien.lenoir@intel.com>
Reviewed-By: Daniel Leidert <dleidert@debian.org>
Origin: https://github.com/u-boot/u-boot/commit/79af75f7776fc20b0d7eb6afe1e27c00fdb4b9b4
Bug: https://github.com/advisories/GHSA-grrh-mjp7-g52c
Bug-Debian: https://bugs.debian.org/983269
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2021-27138
Bug-Freexian-Security: https://deb.freexian.com/extended-lts/tracker/CVE-2021-27138

Gbp-Pq: Name CVE-2021-27138-1.patch