tools: Add gzip-libdeflate advanced compressor

Several devices provide U-Boot versions with only gzip compressed kernel
support (e.g. Realtek switches). This compression method produces larger
images than lzma. To save space on flash and avoid going the hard way with
lzma-loader we can make use of enhanced gzip tool based on libdeflate
compression library from https://github.com/ebiggers/libdeflate. It
keeps 100% deflate/gzip compatibility while improving compression ratio.
The image can be unpacked by the default inflate routines inside U-Boot.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
[Switched to v1.15 and made it work with cmake]
Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Reviewed-by: Robert Marko <robimarko@gmail.com>
Reviewed-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Sander Vanheule <sander@svanheule.net>