iio: humidity: Replace older GPIO APIs with GPIO Consumer APIs for the dht11 sensor

The dht11 driver uses a single gpio to make measurements. It was
using the older global gpio numberspace. The patch replaces the
old gpio api with the new gpio descriptor based api.

Removed header files "linux/gpio.h" and "linux/of_gpio.h"

Signed-off-by: Shobhit Kukreti <shobhitkukreti@gmail.com>
Acked-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>