scripts/image_signing/ensure_amd_psp_flags: Ignore non-AMD images
scripts/image_signing/ensure_amd_psp_flags: Ignore non-AMD images

This commit updates the `ensure_amd_psp_flags` script so that it will
ignore any artifacts that do not contain valid AMD AP images as long as
there are no soft-fuse bitsets present for the given board. This allows
all logic to be contained within this script.

BRANCH=none
BUG=b:202397678
TEST=Verified that script still works on AMD artifacts, tested that
Intel and ARM artifacts are ignored

Change-Id: I17a9414a36fbeb4a0ae9792c2e036deccd089870
Signed-off-by: Robert Zieba <33e0ad3807fbfa18c105b3fe38a4090f81988052@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3860383
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot