gpio: xlp: Convert to immutable irq_chip

Convert the driver to immutable irq-chip with a bit of
intuition.

In this case the driver uses .mask_ack() and .unmask()
and since I have a vague idea about the semantics of
.mask_ack() I added .irq_enable() to the existing .irq_disable()
and called into the gpiolib core from those callbacks
instead of mask/unmask.

Cc: Marc Zyngier <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Reviewed-by: Marc Zyngier <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-xlp.c

···
 	writel(value, addr + regset);
 }
 
+static void xlp_gpio_irq_enable(struct irq_data *d)
+{
+	struct gpio_chip *gc  = irq_data_get_irq_chip_data(d);
+
+	gpiochip_enable_irq(gc, irqd_to_hwirq(d));
+}
+
 static void xlp_gpio_irq_disable(struct irq_data *d)
 {
 	struct gpio_chip *gc  = irq_data_get_irq_chip_data(d);
···
 	xlp_gpio_set_reg(priv->gpio_intr_en, d->hwirq, 0x0);
 	__clear_bit(d->hwirq, priv->gpio_enabled_mask);
 	spin_unlock_irqrestore(&priv->lock, flags);
+	gpiochip_disable_irq(gc, irqd_to_hwirq(d));
 }
 
 static void xlp_gpio_irq_mask_ack(struct irq_data *d)
···
 static struct irq_chip xlp_gpio_irq_chip = {
 	.name		= "XLP-GPIO",
 	.irq_mask_ack	= xlp_gpio_irq_mask_ack,
+	.irq_enable	= xlp_gpio_irq_enable,
 	.irq_disable	= xlp_gpio_irq_disable,
 	.irq_set_type	= xlp_gpio_set_irq_type,
 	.irq_unmask	= xlp_gpio_irq_unmask,
-	.flags		= IRQCHIP_ONESHOT_SAFE,
+	.flags		= IRQCHIP_ONESHOT_SAFE | IRQCHIP_IMMUTABLE,
+	GPIOCHIP_IRQ_RESOURCE_HELPERS,
 };
 
 static void xlp_gpio_generic_handler(struct irq_desc *desc)
···
 	spin_lock_init(&priv->lock);
 
 	girq = &gc->irq;
-	girq->chip = &xlp_gpio_irq_chip;
+	gpio_irq_chip_set_chip(girq, &xlp_gpio_irq_chip);
 	girq->parent_handler = xlp_gpio_generic_handler;
 	girq->num_parents = 1;
 	girq->parents = devm_kcalloc(&pdev->dev, 1,