Fix gcc-4.7 building problem.

Applied function attribute to function definition to avoid 'conflicting type' warning.

Function declaration is in src/include/cpu.h
  void secondary_cpu_init(unsigned int cpu_index)__attribute__((regparm(0)));

But function definition in lapic_cpu_init.c is missing the "__attribute__" part.

Change-Id: Idb7cd00fda5a2d486893f9866920929c685d266e
Signed-off-by: Han Shen <shenhan@google.com>
Reviewed-on: http://review.coreboot.org/1784
Tested-by: build bot (Jenkins)
Reviewed-by: Anton Kochkov <anton.kochkov@gmail.com>

src/include/cpu/cpu.h

@@ -7,7 +7,7 @@
 void cpu_initialize(void);
 struct bus;
 void initialize_cpus(struct bus *cpu_bus);
-void secondary_cpu_init(void);
+void __attribute__((regparm(0))) secondary_cpu_init(void);
 
 #if CONFIG_HAVE_SMI_HANDLER
 void smm_init(void);