As noticed by Mikulas Patocka, the backoff macros don't
completely nop out for UP builds, we still get a
branch always and a delay slot nop.
Fix this by making the branch to the backoff spin loop
selective, then we can nop out the spin loop completely.
Signed-off-by: David S. Miller <davem@davemloft.net>
0f58189d4a