[hmac] Implement a SW reset

[martin-velay]

With the current RTL implementation, it's not possible to interrupt the current operations abruptly and move back into the initial state of the FSMs. Which means that if there is an alert somewhere or if something went wrong we'll have to perform some dummy operations to be able to restart from a suitable state.

Note: I have also heard that this could also be the case for other blocks.

Note: this could also auto-trigger a wipe_secret operation to be sure that nothing sensitive is left.

FYI: @vogelpi, @nasahlpa and @andreaskurth, do you have thoughts about this?