gpio driven authoring process

Step 1. Obtain device node

　　Use of_find_node_by_path acquiring the node information in the device tree

Step 2. Get gpio property

　　Use of_get_named_gpio acquiring attribute information of the device tree gpio

Step 3. Set output mode input

　　Use gpio_direction_output gpio provided as inputs or outputs, and the default level

Step 4. set the output level

　　Use gpio_set_value output level setting gpio