units: also require /dev/tpm0 to be around before tpm2.target can be reached

units: also require /dev/tpm0 to be around before tpm2.target can be reached

While we typically just use /dev/tpmrm0 for accessing the TPM chip (i.e
via the kernel's own resource manager), some sysfs properties that
matter are on /dev/tpm0 only (i.e. the version without the kernel TPM
resource manager). Hence, wait for both to show up in tpm2.target, so
that we can be sure the full API is available.

This matters because we want to access /sys/class/tpm/tpm0/ppi/request
in the next commit.