unicore32: remove unneeded select GENERIC_GPIO

PUV3_GPIO depends on ARCH_PUV3 which requires GPIOLIB and thus already
selects GENERIC_GPIO

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>