[SPARC64]: Use sun4v_cpu_idle() in cpu_idle() on SUN4V.

We have to turn off the "polling nrflag" bit when we sleep
the cpu like this, so that we'll get a cross-cpu interrupt
to wake the processor up from the yield.

We also have to disable PSTATE_IE in %pstate around the yield
call and recheck need_resched() in order to avoid any races.

Signed-off-by: David S. Miller <davem@davemloft.net>