MIPS: VR41xx: Mark GPIO lines used for IRQ

When an IRQ is started on a GPIO line, mark this GPIO as IRQ in
the gpiolib so we can keep track of the usage centrally.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: linux-gpio@vger.kernel.org
Cc: Alexandre Courbot <acourbot@nvidia.com>
Patchwork: https://patchwork.linux-mips.org/patch/6417/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>