Fixes for --assign-lock-ids pass

[newling]

This fixes a few issues with this pass. The issues were

1. hard coded number of locks per tile at 15.
2. in some cases, locks were still being assigned IDs greater than the number of HW locks
3. did not signal failure (just emitted error from op, and returned) to halt pass pipeline

This PR also implements the pass a bit more efficiently (does less work to find a free ID).

[stephenneuendorffer]

Thanks for this!

[stephenneuendorffer]

Thanks!

[makslevental]

@newling is this good to go?

[newling]

@newling is this good to go?

I hope to merge today, got some other things to do first though. Thanks for the comments -- will address.

[newling]

@makslevental and @stephenneuendorffer I don't seem to have write permission -- I'm happy with the current state if you want to go ahead and merge this.

[makslevental]

Done!