x86: Move call64 to the i386 directory

This code is only used in 32-bit mode. Move it so that it does not get
built with 64-bit U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/i386/Makefile b/arch/x86/cpu/i386/Makefile
index d336495..2547bba 100644
--- a/arch/x86/cpu/i386/Makefile
+++ b/arch/x86/cpu/i386/Makefile
@@ -3,5 +3,6 @@
 # Written by Simon Glass <sjg@chromium.org>
 #
 
+obj-y += call64.o
 obj-y += cpu.o
 obj-y += interrupt.o