The IP responsible for the muxing on the Allwinner SoCs are also
handling the GPIOs on the system. This patch adds the needed driver that
relies on the pinctrl driver for most of its operations.

The number of pins available for GPIOs operations are already declared
in the pinctrl driver, we only need to probe a generic driver to handle
the banks available for each SoC.

This driver has been tested on a A13-Olinuxino.
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

The Allwinner SoCs have an IP module that handle both the muxing and the
GPIOs.

This IP has 8 banks of 32 bits, with a number of pins actually useful
for each of these banks varying from one to another, and depending on
the SoC used on the board.

This driver only implements the pinctrl part, the gpio part will come
eventually.
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>