xilinx: zynqmp: Enable DFU tftp support

xilinx: zynqmp: Enable DFU tftp support

Enable DFU tftp support for firmware update. Fill dfu_ram_tftp variable to
have command present for showing how to use it.

boot FIT image has been created from below fragment. Key part is that type
of image has to be firmware. Also based on experiment load property is
completely ignored and base addresses are taken from dfu_alt_info variable.

$ cat update_uboot.its
/dts-v1/;

/ {
	description = "Automatic U-Boot update";
	#address-cells = <1>;

	images {
		Image {
			description = "Kernel";
			data = /incbin/("/tftpboot/Image");
			compression = "none";
			arch = "arm64";
			type = "firmware";
			os = "linux";
			load = <0x80000>;
			entry = <0x80000>;
			hash-1 {
				algo = "sha1";
			};
		};
		system.dtb {
			description = "DTB";
			data = /incbin/("/tftpboot/system.dtb");
			compression = "none";
			arch = "arm64";
			type = "firmware";
			load = <0>;
			hash-1 {
				algo = "sha1";
			};
		};
	};
};

$ mkimage -f update_uboot.its /tftpboot/boot

When U-Boot starts get IP address and server IP.
dhcp
setenv serverip 192.168.0.105

And then run prepared command.
run dfu_ram_tftp

Signed-off-by: Michal Simek <michal.simek@xilinx.com>