Documentation: Fixes some translation error in Documentation/zh_CN/gpio.txt

Fixes some translation error in Documentation/zh_CN/gpio.txt
The modification is based on Dong Aisheng <b29396@freescale.com>'s
corrections:
    1.Two "OUTPUT" is incorrectly translated as "输入";
    2.five improvement of translation;
    3.Delete a redundant paragraph,

Signed-off-by: Fu Wei <tekkamanninja@gmail.com>
Acked-by: Harry Wei <harryxiyou@gmail.com>
Acked-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>