FRV: Implement TIF_NOTIFY_RESUME

Implement the TIF_NOTIFY_RESUME thread flag, making it call do_notify_resume()
which then clears it.  This will be made use of later by tracehooks in the
new-style ptrace implementation

Also discard TIF_IRET as that's not used by FRV.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>