This adds support for seamless booting of Qubes with a TPM disk key,
as well as signing of qubes files in /boot with a Yubikey.
The signed hashes also includes a TPM counter, which is incremented
when new hashes are signed. This prevents rollback attacks against
the /boot filesystem.
The TPMTOTP value is presented to the user at the time of entering
the disk encryption keys. Hitting enter will generate a new code.
The LUKS headers are included in the TPM sealing of the disk
encryption keys.
