UEFI: support for Secure Boot and for SuperMicro+AMI bios
This PR adds support for UEFI Secure boot. It has been tested and deployed in production for about a year on amd64, in a downstream Debian derivative where we do self-signing. The Secure Boot related packages are unchanged from Debian/Ubuntu. It has not been tested on arm64 but at least in Ubuntu the packages and code are exactly the same. It has been tested on various amd64 platforms, including the SuperMicro mentioned in the commit messages, and with Tianocore on Qemu.