gdsys IHS FPGA for CON devices

The gdsys IHS FPGA is the main FPGA on gdsys CON devices. This driver provides
support for enabling and starting the FPGA, as well as verifying working bus
communication.

Required properties:
- compatible: must be "gdsys,iocon_fpga"
- reset-gpios: List of GPIOs controlling the FPGA's reset
- done-gpios: List of GPIOs notifying whether the FPGA's reconfiguration is
              done

Example:

FPGA0 {
	compatible = "gdsys,iocon_fpga";
	reset-gpios = <&PPCPCA 26 0>;
	done-gpios = <&GPIO_VB0 19 0>;
};