MCA: Don't refill the record list during boot.

[markj]

Summary

If we take a CMCI during boot (between SI_SUB_CPU and SI_SUB_CONFIGURE)
before the refill task is initialized, we'll panic otherwise. Instead, predicate use of
the taskqueue on !cold and make sure that we've refilled the record list when starting
the taskqueue thread.

[jhb]

(Rough life if you are getting CMCI's before you can even get to single user)

sys/x86/x86/mca.c

717 ↗

(On Diff #22895)

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