Some of the new units using systemd-pcrphase are missing the --graceful
flag which causes them to error if the tpm libraries are not installed.
Add --graceful just like in the other pcrphase units to make systemd-pcrphase
exit gracefully if the tpm libraries are missing.
These units are also present in the initrd, so instead of an assert,
just use a condition so they are skipped where they need to be skipped.
Fixes https://github.com/systemd/systemd/issues/26358