x86: Use the standard arch_cpu_init() function

Instead of an x86-specific cpu_init_f() function, use the normal U-Boot one
for this purpose. Also remove a useless/misleading comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/include/asm/u-boot-x86.h b/arch/x86/include/asm/u-boot-x86.h
index 89618c7..fdb8a6c 100644
--- a/arch/x86/include/asm/u-boot-x86.h
+++ b/arch/x86/include/asm/u-boot-x86.h
@@ -9,6 +9,7 @@
 #define _U_BOOT_I386_H_	1
 
 /* cpu/.../cpu.c */
+int arch_cpu_init(void);
 int x86_cpu_init_r(void);
 int cpu_init_r(void);
 int x86_cpu_init_f(void);