thermal: hisilicon: fix IRQ imbalance enabling

When register sensors into thermal zone during initialization phase, it
will report error for IRQ imbalance enabling:

[    2.040713] WARNING: at kernel/irq/manage.c:513
[    2.040719] Modules linked in:
[    2.040721]
[    2.040729] CPU: 1 PID: 804 Comm: irq/33-hisi_the Not tainted 4.5.0-rc4+ #505
[    2.040732] Hardware name: HiKey Development Board (DT)
[    2.040736] task: ffffffc03ae82580 ti: ffffffc0379c8000 task.ti: ffffffc0379c8000
[    2.040745] PC is at __enable_irq+0x74/0x84
[    2.040749] LR is at __enable_irq+0x74/0x84

This is caused by enabling IRQ twice. During sensor's initialization
it tries to enable IRQ; but this flow will be preempted by IRQ handler.
Finally introduces race condition between them and the "irq_enabled"
flag will be set to false, so when initialize another sensor, it will
call enable_irq() twice.

hisi_thermal_get_temp()                    hisi_thermal_alarm_irq
  if (max_temp < sensor->thres_temp) {
    data->irq_enabled = true;
	'---------->                         disable_irq_nosync(irq);
                                             data->irq_enabled = false;
    enable_irq(data->irq);   <--------------------------`
  }

This patch is to fix this issue, firstly init "irq_enabled" flag according
to interrupt controller's setting. And also use more strictly
condition so check if need enable the interrupt.

Signed-off-by: Leo Yan <leo.yan@linaro.org>