[xen] Use generic test_and_clear_bit() function

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/include/bits/xen.h

 	return retval;
 }
 
-/**
- * Test and clear pending event
- *
- * @v xen		Xen hypervisor
- * @v port		Event channel port
- * @ret pending		Event was pending
- */
-static inline __attribute__ (( always_inline )) uint8_t
-xenevent_pending ( struct xen_hypervisor *xen, evtchn_port_t port ) {
-	uint8_t pending;
-
-	__asm__ __volatile__ ( "lock btr %2, %0\n\t"
-			       "setc %1\n\t"
-			       : "+m" ( xen->shared->evtchn_pending ),
-				 "=a"  ( pending )
-			       : "Ir" ( port ) );
-	return pending;
-}
-
 #endif /* _BITS_XEN_H */

src/include/ipxe/xen.h

 #define __XEN_INTERFACE_VERSION__ 0x00040400
 
 #include <stdint.h>
+#include <ipxe/bitops.h>
 #include <ipxe/uaccess.h>
 #include <xen/xen.h>
 #include <xen/event_channel.h>
 	struct xen_store store;
 };
 
+/**
+ * Test and clear pending event
+ *
+ * @v xen		Xen hypervisor
+ * @v port		Event channel port
+ * @ret pending		Event was pending
+ */
+static inline __attribute__ (( always_inline )) int
+xenevent_pending ( struct xen_hypervisor *xen, evtchn_port_t port ) {
+
+	return test_and_clear_bit ( port, xen->shared->evtchn_pending );
+}
+
 #include <bits/xen.h>
 
 /**