Same idea as with bootctl, we might be doing image builds from a
system that doesn't boot with UEFI but we still might want to measure
stuff for the image we're building so let's not gate this behind
ENABLE_BOOTLOADER.
bootctl is rather useful to have, even if on a system without UEFI,
as it has a number of verbs that are unrelated to UEFI (e.g kernel-identify),
and more importantly, it supports --root to operate on directory trees
(which could be intended to be deployed on UEFI) so let's make sure we
always build it.
The tool initially just measured the boot phase, but was subsequently
extended to measure file system and machine IDs, too. At AllSystemsGo
there were request to add more, and make the tool generically
accessible.
Hence, let's rename the binary (but not the pcrphase services), to make
clear the tool is not just measureing the boot phase, but a lot of other
things too.
The tool is located in /usr/lib/ and still relatively new, hence let's
just rename the binary and be done with it, while keeping the unit names
stable.
While we are at it, also move the tool out of src/boot/ and into its own
src/pcrextend/ dir, since it's not really doing boot related stuff
anymore.