MIPS: Move Loongson GPIO driver to drivers/gpio

Move Loongson-2's GPIO driver to drivers/gpio and add Kconfig options.

Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

diff --cc arch/mips/configs/lemote2f_defconfig
Simple merge

diff --cc arch/mips/loongson/common/Makefile
Simple merge

diff --cc drivers/gpio/Kconfig
Simple merge

diff --cc drivers/gpio/Makefile
Simple merge

diff --cc drivers/gpio/gpio-loongson.c
Simple merge