[IA64] Fix save/restore

Using the new hypercall path, scratch registers are not saved/restored.

So after returning from hypercall, r20 may contain garbage data.
This triggered General Exception.

Signed-off-by: Anthony Xu <anthony.xu@intel.com>

linux-2.6-xen-sparse/arch/ia64/xen/xensetup.S

@@ -39,7 +39,7 @@ END(early_xen_setup)
    Just force the stacked registers to be written in memory.  */	
 GLOBAL_ENTRY(xencomm_arch_hypercall_suspend)
 	;; 
-	alloc r20=ar.pfs,0,0,2,0
+	alloc r20=ar.pfs,0,0,6,0
 	mov r2=__HYPERVISOR_sched_op
 	;; 
 	/* We don't want to deal with RSE.  */
@@ -49,6 +49,5 @@ GLOBAL_ENTRY(xencomm_arch_hypercall_suspend)
 	;;
 	break 0x1000
 	;; 
-	mov ar.pfs=r20
 	br.ret.sptk.many b0
 END(xencomm_arch_hypercall_suspend)