better io-apic messages

Any janitor want to tackle this request-for-patch? :)

There exists two problems:
a) default io-apic boot messages are quite verbose
b) io-apic bugs and anomalies are common enough that it would be nice to enable additional messages when the user requests them

My preferred solution is
apic=verbose -- enable verbose boot messages (seen in current kernels) apic=debug -- enable all messages, including ones normally hidden by APIC_DEBUG

And the default, without any apic=xxx, would be not to show either set of messages.

This solution hides the messages for those who would rather not see them, but ensures they are available via a boot parameter when kernel developers wish to request additional debug info from a user.