MT7530's LED controller can drive up to 15 LED/GPIOs.

Add support for GPIO control and allow users to use its GPIOs by
setting gpio-controller property in device tree.
Signed-off-by: NDENG Qingfang <dqfext@gmail.com>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>