amd64_edac: do not enable module by default

While at it, fix a link failure when !K8_NB.
Acked-by: Doug Thompson <dougthompson@xmission.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Tested-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>

drivers/edac/Kconfig

@@ -60,11 +60,10 @@ config EDAC_MM_EDAC
 
 config EDAC_AMD64
 	tristate "AMD64 (Opteron, Athlon64) K8, F10h, F11h"
-	depends on EDAC_MM_EDAC && X86 && PCI
-	default m
+	depends on EDAC_MM_EDAC && K8_NB && X86_64 && PCI
 	help
-	Support for error detection and correction on the AMD 64
-	Families of Memory Controllers (K8, F10h and F11h)
+	  Support for error detection and correction on the AMD 64
+	  Families of Memory Controllers (K8, F10h and F11h)
 
 config EDAC_AMD64_ERROR_INJECTION
 	bool "Sysfs Error Injection facilities"