amd64_edac: add a leaner syndrome decoding algorithm

Instead of using the whole syndrome tables for channel decoding, use a
set of eigenvectors with which the tables can be generated to search for
the syndrome in error. The algorithm operates independently of symbol
size and can be used for both x4 and x8 syndromes.
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>