edac: move documentation ABI to ABI/testing/sysfs-devices-edac

The EDAC MC API is currently stored at the wrong place. Move the
parts of the EDAC MC ABI that will be kept to
ABI/testing/sysfs-devices-edac.

The Date: field were added based on git timestamps for the git
commit patches that added the functionality at edac.txt.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>