gpio: Add GPIOLIB_IRQCHIP cleanup to TODO

The GPIOLIB irqchip is a helper irqchip for "simple cases" that should

try to cover any generic kind of irqchip cascaded from a GPIO.

- Convert all the GPIOLIB_IRQCHIP users to pass an irqchip template,

  parent and flags before calling [devm_]gpiochip_add[_data]().

  Currently we set up the irqchip after setting up the gpiochip

  using gpiochip_irqchip_add() and gpiochip_set_[chained|nested]_irqchip().

  This is too complex, so convert all users over to just set up

  the irqchip before registering the gpio_chip, typical example:

  /* Typical state container with dynamic irqchip */

  struct my_gpio {

      struct gpio_chip gc;

      struct irq_chip irq;

  };

  int irq; /* from platform etc */

  struct my_gpio *g;

  struct gpio_irq_chip *girq

  /* Set up the irqchip dynamically */

  g->irq.name = "my_gpio_irq";

  g->irq.irq_ack = my_gpio_ack_irq;

  g->irq.irq_mask = my_gpio_mask_irq;

  g->irq.irq_unmask = my_gpio_unmask_irq;

  g->irq.irq_set_type = my_gpio_set_irq_type;

  /* Get a pointer to the gpio_irq_chip */

  girq = &g->gc.irq;

  girq->chip = &g->irq;

  girq->parent_handler = ftgpio_gpio_irq_handler;

  girq->num_parents = 1;

  girq->parents = devm_kcalloc(dev, 1, sizeof(*girq->parents),

                               GFP_KERNEL);

  if (!girq->parents)

      return -ENOMEM;

  girq->default_type = IRQ_TYPE_NONE;

  girq->handler = handle_bad_irq;

  girq->parents[0] = irq;

  When this is done, we will delete the old APIs for instatiating

  GPIOLIB_IRQCHIP and simplify the code.

- Look over and identify any remaining easily converted drivers and

  dry-code conversions to gpiolib irqchip for maintainers to test