fix build bug in "x86: add PCI extended config space access for AMD Barcelona"

arch/x86/kernel/cpu/amd.c

@@ -4,6 +4,7 @@
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/apic.h>
+#include <asm/mmconfig.h>
 
 #include <mach_apic.h>
 #include "../setup.h"

include/asm-x86/mmconfig.h

@@ -9,6 +9,10 @@ static inline void fam10h_check_enable_mmcfg(void) { }
 static inline void check_enable_amd_mmconf_dmi(void) { }
 #endif
 
+#if defined(CONFIG_SMP) && defined(CONFIG_X86_64)
 extern void __cpuinit amd_enable_pci_ext_cfg(struct cpuinfo_x86 *c);
+#else
+static inline void amd_enable_pci_ext_cfg(struct cpuinfo_x86 *c) { }
+#endif
 
 #endif