x86, amd-nb: Cleanup AMD northbridge caching code

Support more than just the "Misc Control" part of the northbridges.
Support more flags by turning "gart_supported" into a single bit flag
that is stored in a flags member. Clean up related code by using a set
of functions (amd_nb_num(), amd_nb_has_feature() and node_to_amd_nb())
instead of accessing the NB data structures directly. Reorder the
initialization code and put the GART flush words caching in a separate
function.

Signed-off-by: Hans Rosenfeld <hans.rosenfeld@amd.com>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
diff --git a/drivers/edac/amd64_edac.c b/drivers/edac/amd64_edac.c
index 8b144cc..774f950 100644
--- a/drivers/edac/amd64_edac.c
+++ b/drivers/edac/amd64_edac.c
@@ -2917,7 +2917,7 @@
 
 	opstate_init();
 
-	if (cache_amd_northbridges() < 0)
+	if (amd_cache_northbridges() < 0)
 		goto err_ret;
 
 	msrs = msrs_alloc();
@@ -2934,7 +2934,7 @@
 	 * to finish initialization of the MC instances.
 	 */
 	err = -ENODEV;
-	for (nb = 0; nb < amd_northbridges.num; nb++) {
+	for (nb = 0; nb < amd_nb_num(); nb++) {
 		if (!pvt_lookup[nb])
 			continue;