MAINTAINERS: Add Tony and Boris as ACPI/APEI reviewers

Since this piece of the ACPI pile is doing RAS, it is perhaps prudent if
we at least paid attention to it and the direction it takes. So add Tony
and me as reviewers.

Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>