x86: extract common part of head32.c and head64.c into head.c

This patch extracts the common part of head32.c and head64.c into head.c.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: andi@firstfloor.org
Cc: mingo@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 3cff3c8..30b046b 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -160,6 +160,7 @@
 
 head-y := arch/x86/kernel/head_$(BITS).o
 head-y += arch/x86/kernel/head$(BITS).o
+head-y += arch/x86/kernel/head.o
 head-y += arch/x86/kernel/init_task.o
 
 libs-y  += arch/x86/lib/