x86: Support QEMU x86 targets

This commit introduces the initial U-Boot support for QEMU x86 targets.
U-Boot can boot from coreboot as a payload, or directly without coreboot.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Merged in patch 'x86: qemu: Add CMD_NET to qemu-x86_defconfig
   https://patchwork.ozlabs.org/patch/479745/

include/configs/qemu-x86.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2015, Bin Meng <bmeng.cn@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/*
+ * board/config.h - configuration options, board specific
+ */
+
+#ifndef __CONFIG_H
+#define __CONFIG_H
+
+#include <configs/x86-common.h>
+
+#define CONFIG_SYS_MONITOR_LEN		(1 << 20)
+
+#define CONFIG_NR_DRAM_BANKS		1
+
+#define CONFIG_X86_SERIAL
+
+#define CONFIG_PCI_MEM_BUS		0xc0000000
+#define CONFIG_PCI_MEM_PHYS		CONFIG_PCI_MEM_BUS
+#define CONFIG_PCI_MEM_SIZE		0x10000000
+
+#define CONFIG_PCI_PREF_BUS		0xd0000000
+#define CONFIG_PCI_PREF_PHYS		CONFIG_PCI_PREF_BUS
+#define CONFIG_PCI_PREF_SIZE		0x10000000
+
+#define CONFIG_PCI_IO_BUS		0x2000
+#define CONFIG_PCI_IO_PHYS		CONFIG_PCI_IO_BUS
+#define CONFIG_PCI_IO_SIZE		0xe000
+
+#define CONFIG_PCI_PNP
+#define CONFIG_E1000
+
+#define CONFIG_STD_DEVICES_SETTINGS	"stdin=serial\0" \
+					"stdout=serial\0" \
+					"stderr=serial\0"
+
+#define CONFIG_SCSI_DEV_LIST		\
+	{PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_82371SB_1}
+
+/* GPIO is not supported */
+#undef CONFIG_INTEL_ICH6_GPIO
+#undef CONFIG_CMD_GPIO
+
+/* SPI is not supported */
+#undef CONFIG_ICH_SPI
+#undef CONFIG_ENV_IS_IN_SPI_FLASH
+#define CONFIG_ENV_IS_NOWHERE
+
+/* Video is not supported */
+#undef CONFIG_VIDEO
+#undef CONFIG_CFB_CONSOLE
+
+#endif	/* __CONFIG_H */