Check for powerpc64 cores that fail to start

Check for powerpc64 cores that fail to start

If the core failed to start (because opal_start_cpu didn't return
OPAL_SUCCESS), or failed to identify, then don't use the core.

Eduardo Pires told ppc@ in April 2023 about a machine that froze at
boot; cpu1 had failed to start with error -14 OPAL_WRONG_STATE.  See
https://marc.info/?l=openbsd-ppc&m=168106893329069&w=2

ok miod@