Create default gpio base if neither device node nor
platform data is defined.

Cc: Stable <stable@vger.kernel.org>
Signed-off-by: NSonic Zhang <sonic.zhang@analog.com>
Reviewed-by: NAlexandre Courbot <acourbot@nvidia.com>
Tested-by: NAntonio Fiol <antonio@fiol.es>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>