mca: Some error handling logic improvements.

• Enable local MCEs on capable Intel CPUs. It delivers exceptions

only to the affected CPU instead of global broadcast, requiring a lot
of synchronization between CPUs. AMD always deliver MCEs locally.

• Make MCE handler process only uncorrected errors, while CMCI and

polling only corrected. It reduces synchronization problems between
them and is explicitly recommended by the documentation.

• Add minimal support for uncorrected software recoverable errors

on Intel CPUs. It allows to avoid kernel panics in case uncorrected
errors do not affect current operation, like ones found during scrub
or write. Such errors are only logged, postponing the panic until
the corrupted data will actually be needed (that may never happen).

• Reduce polling period from 1 hour to 5 minutes.

MFC after: 2 weeks