gpio: davinci: Use unique labels for each gpio chip

The gpiod framework uses the chip label to match a specific chip.
The davinci gpio driver, creates several chips using always the same
label, which is not compatible with gpiod.

To allow platform data to declare gpio lookup tables, and for drivers
to use the gpiod framework, allocate unique label per registered chip.

Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
Reviewed-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>