MIPS: OCTEON: Select ARCH_REQUIRE_GPIOLIB

... and create asm/mach-cavium-octeon/gpio.h so that things continue
to build.

This allows us to use the existing I2C connected GPIO expanders.

Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/5632/


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