x86: Make QEMU the default vendor

Now that we have QEMU support, make it the default vendor in the
'make menuconfig' screen.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3d02620..0b78f10 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -12,7 +12,7 @@
 
 choice
 	prompt "Mainboard vendor"
-	default VENDOR_COREBOOT
+	default VENDOR_EMULATION
 
 config VENDOR_COREBOOT
 	bool "coreboot"