gpio: loongson: Use right include

The driver includes <linux/gpio.h> which is wrong, rely on
<linux/gpio/driver.h> and remove to call to gpio_set_value() in
favor of calling the internal function. Move functions around to
avoid forward declarations.

Cc: Keguang Zhang <keguang.zhang@gmail.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: linux-mips@linux-mips.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>