x86, alternative: Use .pushsection/.popsection

.section/.previous doesn't nest.  Use .pushsection/.popsection in
<asm/alternative.h> so that they can be properly nested.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-5-git-send-email-hpa@linux.intel.com
diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 952bd01..018d29f 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -5,10 +5,10 @@
 #ifdef CONFIG_SMP
 	.macro LOCK_PREFIX
 672:	lock
-	.section .smp_locks,"a"
+	.pushsection .smp_locks,"a"
 	.balign 4
 	.long 672b - .
-	.previous
+	.popsection
 	.endm
 #else
 	.macro LOCK_PREFIX