Flash device on Cortina Systems Gemini SoC

This flash is regular CFI compatible (Intel or AMD extended) flash chips with
some special bits that can be controlled by the machine's system controller.

Required properties:
- compatible : must be "cortina,gemini-flash", "cfi-flash";
- reg : memory address for the flash chip
- syscon : must be a phandle to the system controller
- bank-width : width in bytes of flash interface, should be <2>

For the rest of the properties, see mtd-physmap.yaml.

The device tree may optionally contain sub-nodes describing partitions of the
address space. See partition.txt for more detail.

Example:

flash@30000000 {
	compatible = "cortina,gemini-flash", "cfi-flash";
	reg = <0x30000000 0x01000000>;
	syscon = <&syscon>;
	bank-width = <2>;
};