leds: leds-gpio: adopt pinctrl support

Adopt pinctrl support to leds-gpio driver based on leds-gpio
device pointer, pinctrl driver configure SoC pins to GPIO
mode according to definitions provided in .dts file.

Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Acked-by: Marek Vasut <marex@denx.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>