amd64_edac: Add support for interleaved region swapping

On revC3 and revE Fam10h machines and later, non-interleaved graphics
framebuffer memory under the 16G mark can be swapped with a region
located at the bottom of memory so that the GPU can use the interleaved
region and thus two channels. Add support for that.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>