tpm2-util: rename json field "tpm2-pcrlock" → "tpm2_pcrlock"

tpm2-util: rename json field "tpm2-pcrlock" → "tpm2_pcrlock"

We generally want to avoid to include dashes in json field names. We
historically made a mistake there which is hard to fix. But for new
fields, let's get this right. We already got it right for a bunch of new
fields, hence also make sure to use underscores rather dashes for new
additions.

This field was added post v254, and since we didn't release since then,
let's just rename it.