This allows allows shortcutting measurements of the specified files and
use the information from /sys/ instead.
This is not too useful on its own given that "systemd-measure status"
already exists which displays the current, relevant PCR values. The main
difference is how "complete" the information is. "status" will detect if
the measurements make any sense, and show more than PCR 11. "calculate
--current" otoh only reads PCR 11 and uses that, and that's really it.
This is mainly preparation for later work to add PCR signing to the
tool, where usually it makes most sense to sign prepared kernel images,
but for testing it's really useful to shortcut signing to the current
PCR values instead
For now, this simply outputs the PCR hash values expected for a kernel
image, if it's measured like sd-stub would do it.
(Later on, we can extend the tool, to optionally sign these
pre-calculated measurements, in order to implement signed PCR policies
for disk encryption.)
