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/sh/include/asm/thread_info.h

@@ -206,6 +206,9 @@ static inline bool test_and_clear_restore_sigmask(void)
 	ti->status &= ~TS_RESTORE_SIGMASK;
 	return true;
 }
+
+#define tsk_is_polling(t) test_tsk_thread_flag(t, TIF_POLLING_NRFLAG)
+
 #endif	/* !__ASSEMBLY__ */
 
 #endif /* __KERNEL__ */