x86: Fix up some missing prototypes

Some functions are missing prototypes. Fix those that are specific to x86.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/cpu.c b/arch/x86/cpu/cpu.c
index d6ba246..6441dde 100644
--- a/arch/x86/cpu/cpu.c
+++ b/arch/x86/cpu/cpu.c
@@ -197,14 +197,13 @@
 	"generate_gpf:\n"
 	"ljmp   $0x70, $0x47114711\n");
 
-void __reset_cpu(ulong addr)
+__weak void reset_cpu(ulong addr)
 {
 	printf("Resetting using x86 Triple Fault\n");
 	set_vector(13, generate_gpf);	/* general protection fault handler */
 	set_vector(8, generate_gpf);	/* double fault handler */
 	generate_gpf();			/* start the show */
 }
-void reset_cpu(ulong addr) __attribute__((weak, alias("__reset_cpu")));
 
 int dcache_status(void)
 {