gdsys soc bus driver

This driver provides a simple interface for the busses associated with gdsys
IHS FPGAs. The bus itself contains devices whose register maps are contained
within the FPGA's register space.

Required properties:
- fpga: A phandle to the controlling IHS FPGA

Example:

FPGA0BUS: fpga0bus {
	compatible = "gdsys,soc";
	ranges = <0x0 0xe0600000 0x00004000>;
	fpga = <&FPGA0>;
};