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/
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8e734fd..3d02620 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -17,6 +17,9 @@
 config VENDOR_COREBOOT
 	bool "coreboot"
 
+config VENDOR_EMULATION
+	bool "emulation"
+
 config VENDOR_GOOGLE
 	bool "Google"
 
@@ -27,6 +30,7 @@
 
 # board-specific options below
 source "board/coreboot/Kconfig"
+source "board/emulation/Kconfig"
 source "board/google/Kconfig"
 source "board/intel/Kconfig"
 
@@ -34,6 +38,7 @@
 source "arch/x86/cpu/baytrail/Kconfig"
 source "arch/x86/cpu/coreboot/Kconfig"
 source "arch/x86/cpu/ivybridge/Kconfig"
+source "arch/x86/cpu/qemu/Kconfig"
 source "arch/x86/cpu/quark/Kconfig"
 source "arch/x86/cpu/queensbay/Kconfig"