x86: do not use i386 code for x86_64 memory functions

arch/x86/lib/string.c contains assembler implementations of memcpy(),
memmove(), and memset() written for i386. Don't use it on x86_64.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 1e8efcc..56fd680 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -7,6 +7,7 @@
 obj-y += bios.o
 obj-y += bios_asm.o
 obj-y += bios_interrupts.o
+obj-y += string.o
 endif
 ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_CMD_BOOTM) += bootm.o
@@ -32,7 +33,6 @@
 obj-$(CONFIG_INTEL_MID) += scu.o
 obj-y	+= sections.o
 obj-y += sfi.o
-obj-y	+= string.o
 obj-y	+= acpi.o
 obj-$(CONFIG_HAVE_ACPI_RESUME) += acpi_s3.o
 ifndef CONFIG_QEMU