We currently use the ipxe-signer container for the step that combines
the BIOS and UEFI build artifacts to produce the multi-architecture
ISO and USB images.
Switch to using the generic architecture-independent utility toolchain
container, thereby allowing the ipxe-signer container to minimise its
attack surface by removing tools that are not required for the signing
operation.
Signed-off-by: Michael Brown <mcb30@ipxe.org>