Add ASID and context compare for triggers (#363)

* Add tasid in textra (ASID compare for triggers)

There was some e-mail discussion, subject:"ContextID trigger/trace"

* Review feedback/language tweaks.

* textra is present conditional on trigger type.

* Add context registers.

Still allow triggering on ASID as well. Also leave space for future H
mode support.

* Address review feedback.