xen: use hypercall rather than clts

Xen will trap and emulate clts, but its better to use a hypercall.
Also, xenner doesn't handle clts.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/asm-x86/xen/hypercall.h b/include/asm-x86/xen/hypercall.h
index c2ccd99..897ff79 100644
--- a/include/asm-x86/xen/hypercall.h
+++ b/include/asm-x86/xen/hypercall.h
@@ -315,6 +315,13 @@
 }
 
 static inline void
+MULTI_fpu_taskswitch(struct multicall_entry *mcl, int set)
+{
+	mcl->op = __HYPERVISOR_fpu_taskswitch;
+	mcl->args[0] = set;
+}
+
+static inline void
 MULTI_update_va_mapping(struct multicall_entry *mcl, unsigned long va,
 			pte_t new_val, unsigned long flags)
 {