x86: Allow cpu-x86 driver to be probed for UP

Currently cpu-x86 driver is probed only for SMP. We add the same
support for UP when there is only one cpu node in the deive tree.

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

arch/x86/cpu/cpu.c

@@ -696,6 +696,15 @@ __weak int x86_init_cpus(void)
 #ifdef CONFIG_SMP
 	debug("Init additional CPUs\n");
 	x86_mp_init();
+#else
+	struct udevice *dev;
+
+	/*
+	 * This causes the cpu-x86 driver to be probed.
+	 * We don't check return value here as we want to allow boards
+	 * which have not been converted to use cpu uclass driver to boot.
+	 */
+	uclass_first_device(UCLASS_CPU, &dev);
 #endif
 
 	return 0;