gpio: store reflect the label to userspace

The gpio_chip label is useful for userspace to understand what
kind of GPIO chip it is dealing with. Let's store a copy of this
label in the gpio_device, add it to the struct passed to userspace
for GPIO_GET_CHIPINFO_IOCTL and modify lsgpio to show it.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/uapi/linux/gpio.h

@@ -16,10 +16,12 @@
 /**
  * struct gpiochip_info - Information about a certain GPIO chip
  * @name: the name of this GPIO chip
+ * @label: a functional name for this GPIO chip
  * @lines: number of GPIO lines on this chip
  */
 struct gpiochip_info {
 	char name[32];
+	char label[32];
 	__u32 lines;
 };