edac: move EDAC device definitions to drivers/edac/edac_device.h

The edac_core.h header contain data structures and function
definitions for both EDAC MC and EDAC device.

Let's move the devices ones to a separate header file, as part
of a header reorganization.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>