dt-bindings: gpio: add QIXIS FPGA based GPIO controller

Add a device tree binding for the QIXIS FPGA based GPIO controller.
Depending on the board, the QIXIS FPGA exposes registers which act as a
GPIO controller, each with 8 GPIO lines of fixed direction.

Since each QIXIS FPGA layout has its particularities, add a separate
compatible string for each board/GPIO register combination supported.

Since these GPIO controllers are trivial, make use of the newly added
trivial-gpio.yaml file instead of creating an entirely new one.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>