x86: dm: Clean up cpu drivers

This commit does the following to clean up x86 cpu dm drivers:
- Move cpu_x86 driver codes from arch/x86/cpu/cpu.c to a dedicated
  file arch/x86/cpu/cpu_x86.c
- Rename x86_cpu_get_desc() to cpu_x86_get_desc() to keep consistent
  naming with other dm drivers
- Add a new cpu_x86_bind() in the cpu_x86 driver which does exactly
  the same as the one in the intel baytrail cpu driver
- Update intel baytrail cpu driver to use cpu_x86_get_desc() and
  cpu_x86_bind()

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

arch/x86/include/asm/cpu_x86.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2015, Bin Meng <bmeng.cn@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _ASM_CPU_X86_H
+#define _ASM_CPU_X86_H
+
+/**
+ * cpu_x86_bind() - Bind an x86 CPU with the driver
+ *
+ * This updates cpu device's platform data with information from device tree,
+ * like the processor local apic id.
+ *
+ * @dev:	Device to check (UCLASS_CPU)
+ * @return	0 always
+ */
+int cpu_x86_bind(struct udevice *dev);
+
+/**
+ * cpu_x86_get_desc() - Get a description string for an x86 CPU
+ *
+ * This uses cpu_get_name() and is suitable to use as the get_desc() method for
+ * the CPU uclass.
+ *
+ * @dev:	Device to check (UCLASS_CPU)
+ * @buf:	Buffer to place string
+ * @size:	Size of string space
+ * @return:	0 if OK, -ENOSPC if buffer is too small, other -ve on error
+ */
+int cpu_x86_get_desc(struct udevice *dev, char *buf, int size);
+
+#endif /* _ASM_CPU_X86_H */