x86: use asmlinkage macro for smm_handler_t

The smm_handler_t type was added before the introduction
of the asmlinkage macro. Now that asmlinkage is available
use it.

Change-Id: I85ec72cf958bf4b77513a85faf6d300c781af603
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/3215
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)

src/include/cpu/x86/smm.h

@@ -33,6 +33,7 @@
 #define SMM_ENTRY_OFFSET 0x8000
 #define SMM_SAVE_STATE_BEGIN(x) (SMM_ENTRY_OFFSET + (x))
 
+#include <arch/cpu.h>
 #include <types.h>
 typedef struct {
 	u16	es_selector;
@@ -429,7 +430,7 @@ struct smm_runtime {
 	u8 apic_id_to_cpu[CONFIG_MAX_CPUS];
 } __attribute__ ((packed));
 
-typedef void __attribute__((cdecl)) (*smm_handler_t)(void *arg, int cpu,
+typedef void asmlinkage (*smm_handler_t)(void *arg, int cpu,
                                          const struct smm_runtime *runtime);
 
 #ifdef __SMM__