x86: Make x86_init_cpus() static

There are no other implementations of this function, and boards that need it
can implement a CPU driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/include/asm/u-boot-x86.h

@@ -77,8 +77,6 @@ uint64_t timer_get_tsc(void);
 
 void quick_ram_check(void);
 
-int x86_init_cpus(void);
-
 #define PCI_VGA_RAM_IMAGE_START		0xc0000
 
 #endif	/* _U_BOOT_I386_H_ */