APEI: Improve multiple error sources handling.

Some AMD systems I have report 8 NMI and 3591 polled error sources.
Previous code could handle only one NMI source and used separate
callout for each polled source. New code can handle multiple NMIs
and groups polled sources by power of 2 of the polling period.

MFC after: 2 weeks

(cherry picked from commit 2dfc1f73552d5aa5d9f6fa3e642f00e87952551c)