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>