units: retitle systemd-pcrextend.{service,socket}, change TPM2→TPM

units: retitle systemd-pcrextend.{service,socket}, change TPM2→TPM

I was looking at the logs in some bug and saw this:

Mar 13 15:55:12 fedora systemd[1]: systemd-pcrmachine.service - TPM2 PCR Machine ID Measurement was skipped because of an unmet condition check (ConditionSecurity=measured-uki).
Mar 13 15:55:12 fedora systemd[1]: Starting systemd-remount-fs.service - Remount Root and Kernel File Systems...
Mar 13 15:55:12 fedora systemd[1]: systemd-tpm2-setup-early.service - TPM2 SRK Setup (Early) was skipped because of an unmet condition check (ConditionSecurity=measured-uki).

This is overly technical, for most units we don't provide this level of
detail about the implementation. So retitle the units to be more accessible.

Also, the fact that it's a v. 2 of the TPM is not that important. We don't
support TPM 1.2, but computers without TPM v2 are getting rare. For other
units we don't advertise the version of hardware, and let's not do this here,
to reduce some complexity.