x86: kconfig: Select ARCH_EARLY_INIT_R in the platform Kconfig

This is architecture-dependent early initialization hence should
be put in the platform Kconfig.

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

board/coreboot/coreboot/Makefile

@@ -12,4 +12,4 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-y	+= coreboot_start.o coreboot.o
+obj-y	+= coreboot_start.o

board/coreboot/coreboot/coreboot.c

@@ -1,14 +0,0 @@
-/*
- * Copyright (C) 2013 Google, Inc
- *
- * SPDX-License-Identifier:	GPL-2.0+
- */
-
-#include <common.h>
-#include <cros_ec.h>
-#include <asm/gpio.h>
-
-int arch_early_init_r(void)
-{
-	return 0;
-}