intel_idle: allow idle states to be freeze-mode specific

intel_idle uses a NULL "enter" field in a cpuidle state
to recognize the invalid entry terminating a variable-length array.

Linux-4.0 added support for the system-wide "freeze" state
in cpuidle drivers via the new "enter_freeze" field.

The natural way to expose a deep idle state for freeze,
but not for run-time idle is to supply "enter_freeze" without "enter";
so we update the driver to accept such states.
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/idle/intel_idle.c

@@ -965,7 +965,8 @@ static int __init intel_idle_cpuidle_driver_init(void)
 	for (cstate = 0; cstate < CPUIDLE_STATE_MAX; ++cstate) {
 		int num_substates, mwait_hint, mwait_cstate;
 
-		if (cpuidle_state_table[cstate].enter == NULL)
+		if ((cpuidle_state_table[cstate].enter == NULL) &&
+		    (cpuidle_state_table[cstate].enter_freeze == NULL))
 			break;
 
 		if (cstate + 1 > max_cstate) {