x86: qemu: Support operation as an EFI payload

Disable a few things which interfere with the EFI init. This allows QEMU to
to boot into EFI, load a U-Boot payload then boot to the U-Boot prompt.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/qemu/Makefile b/arch/x86/cpu/qemu/Makefile
index be79723..9a66b16 100644
--- a/arch/x86/cpu/qemu/Makefile
+++ b/arch/x86/cpu/qemu/Makefile
@@ -4,5 +4,8 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-y += car.o dram.o qemu.o
+ifndef CONFIG_EFI_STUB
+obj-y += car.o dram.o
+endif
+obj-y += qemu.o
 obj-$(CONFIG_PCI) += pci.o