sanitize tsk_is_polling()

Make default just return 0.  The current default (checking
TIF_POLLING_NRFLAG) is taken to architectures that need it;
ones that don't do polling in their idle threads don't need
to defined TIF_POLLING_NRFLAG at all.

ia64 defined both TS_POLLING (used by its tsk_is_polling())
and TIF_POLLING_NRFLAG (not used at all).  Killed the latter...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/mn10300/include/asm/thread_info.h

@@ -165,6 +165,8 @@ void arch_release_thread_info(struct thread_info *ti);
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */
 
+#define tsk_is_polling(t) test_tsk_thread_flag(t, TIF_POLLING_NRFLAG)
+
 #endif /* __KERNEL__ */
 
 #endif /* _ASM_THREAD_INFO_H */