Impact: Fix marginal race condition

One the first CPU the machine checks are enabled early before
the local APIC is enabled. This could in theory lead
to some lost CMCI events very early during boot because
CMCIs cannot be delivered with disabled LAPIC.

The poller also doesn't recover from this because it doesn't
check CMCI banks.

Add an explicit CMCI banks check after the LAPIC is enabled.
This is only done for CPU #0, the other CPUs only initialize
machine checks after the LAPIC is on.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>