gdsys IO endpoint of IHS FPGA devices

The IO endpoint of IHS FPGA devices is a packet-based transmission interface
that allows interconnected gdsys devices to send and receive data over the
FPGA's main ethernet connection.

Required properties:
- compatible: must be "gdsys,io-endpoint"
- reg: describes the address and length of the endpoint's register map (within
  the FPGA's register space)

Example:

fpga0_ep0 {
	compatible = "gdsys,io-endpoint";
	reg = <0x020 0x10
           0x320 0x10
           0x340 0x10
           0x360 0x10>;
};