xen64: add 64-bit assembler

Split xen-asm into 32- and 64-bit files, and implement the 64-bit
variants.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
index 2ba2d16..59c1e53 100644
--- a/arch/x86/xen/Makefile
+++ b/arch/x86/xen/Makefile
@@ -1,4 +1,4 @@
 obj-y		:= enlighten.o setup.o multicalls.o mmu.o \
-			time.o xen-asm.o grant-table.o suspend.o
+			time.o xen-asm_$(BITS).o grant-table.o suspend.o
 
 obj-$(CONFIG_SMP)	+= smp.o