x86: efi: payload: Enforce toolchain to generate 64-bit EFI payload stub codes

Attempting to use a toolchain that is preconfigured to generate code
for the 32-bit architecture (i386), for example, the i386-linux-gcc
toolchain on kernel.org, to compile the 64-bit EFI payload does not
build. This updates the makefile fragments to ensure '-m64' is passed
to toolchain when building the 64-bit EFI payload stub codes.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/Makefile b/arch/x86/cpu/Makefile
index d5a17d0..af9e26c 100644
--- a/arch/x86/cpu/Makefile
+++ b/arch/x86/cpu/Makefile
@@ -18,7 +18,8 @@
 ifndef CONFIG_$(SPL_)X86_64
 AFLAGS_REMOVE_call32.o := -mregparm=3 \
 	$(if $(CONFIG_EFI_STUB_64BIT),-march=i386 -m32)
-AFLAGS_call32.o := -fpic -fshort-wchar
+AFLAGS_call32.o := -fpic -fshort-wchar \
+	$(if $(CONFIG_EFI_STUB_64BIT),-m64)
 
 extra-y += call32.o
 endif