gpio: add QIXIS FPGA GPIO controller

gpio: add QIXIS FPGA GPIO controller

Add support for the GPIO controller found on some QIXIS FPGAs in
Layerscape boards such as LX2160ARDB and LS1046AQDS. This driver is
using gpio-regmap.

A GPIO controller has a maximum of 8 lines (all found in the same
register). Even within the same controller, the GPIO lines' direction is
fixed, which mean that both input and output lines are found in the same
register. This is why the driver also passed to gpio-regmap the newly
added .fixed_direction_output bitmap to represent the true direction of
the lines.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Michael Walle <mwalle@kernel.org> # for the gpio-regmap part
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>