busses like i2c, spi and so on can parse the virq of their subnode automatically by
irq_of_parse_and_map(). for example, i2c will do that in of_i2c_register_devices().
people can put hwirq number attached to a gpio controller in dts, and drivers can
directly request the parsed virq.

for example, for an i2c client as below,
tangoc-ts@5c{
	compatible = "pixcir,tangoc-ts";
	interrupt-parent = <&gpio>;
	interrupts = <3 0>;
	reg = <0x5c>;
};
in i2c client probe(), it will request_irq(client->irq, ...) without
calling gpio_direction_input().
so here when we set irq type, we also put the pin to input direction.
Signed-off-by: NBarry Song <Baohua.Song@csr.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>