ACPI: APEI: Add BERT error log footer

Print total number of records found during BERT log parsing.
This also simplify dmesg parser implementation for BERT events.

Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Acked-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>