input: Add a device pointer to the input config

input: Add a device pointer to the input config

The read_keys() method in input is passed a struct input_config. Add a
device pointer there so that we can find out the device that is referred
to with driver model.

Once all drivers are converted we can update the input structure to use
driver model instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>