profiles: Enable TPM2 support in systemd

[pothos]

We could use systemd-cryptenroll and cryptsetup with a TPM device but so far the support was not compiled in.
Enable the use flags for TPM2 support in systemd.

How to use

Testing done

systemd-cryptenroll works with a tpm but so far I didn't manage to make the systemd-cryptsetup generator unlock with a TPM

[ader1990]

There is a cyclical dep between the app-crypt/tpm-tss and virtual/tmpfiles and systemd. Need to see how to break it somehow:

  * Error: circular dependencies:
 
 (app-crypt/tpm2-tss-4.0.1:0/4::portage-stable, ebuild scheduled for merge to '/build/amd64-usr/') depends on
  (virtual/tmpfiles-0-r5:0/0::portage-stable, ebuild scheduled for merge to '/build/amd64-usr/') (runtime)
   (sys-apps/systemd-255.3:0/2::coreos, ebuild scheduled for merge to '/build/amd64-usr/') (runtime)
    (app-crypt/tpm2-tss-4.0.1:0/4::portage-stable, ebuild scheduled for merge to '/build/amd64-usr/') (buildtime_slot_op)

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/8418960061

[pothos]

One way could be using TMPFILES_OPTIONAL=1 in tpm2-tss, the other could be to add an entry in the break_dep_loop list in build_packages (Edit: Trying the break_dep_loop now)

[ader1990]

As Flatcar always uses systemd, we can make this package purely virtual to just flag the usage of the tmpfiles eclass. This can be done by removing the systemd dependency. Might be useful in the future to not have this kind of dependency breaking hacks for other packages too.