edac: move documentation from edac_device to edac_core.h

Several functions are documented at edac_device.c.

As we'll be including edac_core.h at drivers-api book, move those,
in order for the kernel-doc markups be part of the API
documentation book.

As several of those kernel-doc macros are not in the right format,
fix them.

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