cpu/Makefile.inc: Only inculde x86 subdir if ARCH_x86 is selected

There is no other guard to prevent this from being picked up when
building for other architectures.

Change-Id: I2039a289a4dd9970d5dd0f90d43d5d5c2a6d0a0b
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/11795
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/cpu/Makefile.inc b/src/cpu/Makefile.inc
index 92024f3..9220a8a 100644
--- a/src/cpu/Makefile.inc
+++ b/src/cpu/Makefile.inc
@@ -9,7 +9,7 @@
 subdirs-y += intel
 subdirs-y += ti
 subdirs-y += via
-subdirs-y += x86
+subdirs-$(CONFIG_ARCH_X86) += x86
 subdirs-$(CONFIG_CPU_QEMU_X86) += qemu-x86
 
 $(eval $(call create_class_compiler,cpu_microcode,x86_32))