MIPS: Alchemy: add gpio_request/gpio_free stubs for CONFIG_GPIOLIB=n

Some drivers use gpio_request/gpio_free regardless of whether
gpiolib is actually built;  add stubs to work around the ensuing
compile failures.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Tested-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>