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>

arch/x86/Kconfig

@@ -12,7 +12,7 @@ config SYS_VSNPRINTF
 
 choice
 	prompt "Mainboard vendor"
-	default VENDOR_COREBOOT
+	default VENDOR_EMULATION
 
 config VENDOR_COREBOOT
 	bool "coreboot"

configs/coreboot-x86_defconfig

 CONFIG_X86=y
+CONFIG_VENDOR_COREBOOT=y
 CONFIG_TARGET_COREBOOT=y
 CONFIG_CMD_NET=y
 CONFIG_OF_CONTROL=y