Updating Secure Boot dbx with fwupd and the LVFS

BootHole woke a lot of people up to the fact that we don't have a a well-tested approach to updating the UEFI revocation list on Linux systems that doesn't involve crossing your fingers and hoping for the best.

My experience with fwupd and LVFS for handling Lenovo firmware on Thinkpads without a Windows partition has been fairly positive, so I'm hopeful that this experiment will have good results.