x86, bts: exclude ds.c from build when disabled

Impact: cleanup

Move the CONFIG guard from the .c file into the makefile.
Reported-by: NAndi Kleen <andi-suse@firstfloor.org>
Signed-off-by: NMarkus Metzger <markus.t.metzger@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/Makefile

@@ -41,7 +41,7 @@ obj-$(CONFIG_X86_TRAMPOLINE)	+= trampoline.o
 obj-y				+= process.o
 obj-y				+= i387.o xsave.o
 obj-y				+= ptrace.o
-obj-y				+= ds.o
+obj-$(CONFIG_X86_DS)		+= ds.o
 obj-$(CONFIG_X86_32)		+= tls.o
 obj-$(CONFIG_IA32_EMULATION)	+= tls.o
 obj-y				+= step.o

arch/x86/kernel/ds.c

@@ -21,8 +21,6 @@
  */
 
 
-#ifdef CONFIG_X86_DS
-
 #include <asm/ds.h>
 
 #include <linux/errno.h>
@@ -878,4 +876,3 @@ void ds_free(struct ds_context *context)
 	while (leftovers--)
 		ds_put_context(context);
 }
-#endif /* CONFIG_X86_DS */