Staging: iio: adt7316: Add all irq related code in adt7316_irq_setup()

ADT7316 driver no more uses platform data and hence use device tree
data instead of platform data for assigning irq_type field and
implement this in adt7316_irq_setup function.
Switch case figures out the type of irq and if it's the default case
then assign the default value to the irq_type i.e.
irq_type = IRQF_TRIGGER_LOW
Move devm_request_threaded_irq() and assignment of chip->config1
into the adt7316_setup_irq() to unclutter the code in probe function.

Signed-off-by: Shreeya Patel <shreeya.patel23498@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>