usr.bin/pmcstat: Provide a somewhat functional pmcstat -L

[arichardson]

Previously pmcstat -L would return an error, now it returns the list of Neoverse-N1 counters. These are all valid, but we are still missing the Morello-specific counters here.

[bsdjhb]

Hmmm, can you still use Morello-specific counters by name after this change? The pmcstat code around the pmu-events stuff is rather confusing and I couldn't tell if you get the union if both sources (pmu-events and built-in tables) provide events, or if you only get the pmu-events.

[jrtc27]

pmccontrol -L does work to list things today, kinda sad that pmcstat -L can't at least fall back to the built-in tables :(

[arichardson]

pmccontrol -L does work to list things today, kinda sad that pmcstat -L can't at least fall back to the built-in tables :(

Hmm interesting - I was not aware of pmccontrol -L. It looks like this change overrides the list pmccontrol produces, so we can't see all the events.