libkmod: Add ELF notes to compression libraries

libkmod: Add ELF notes to compression libraries

Follow the new spec for ELF notes as detailed in
https://systemd.io/ELF_PACKAGE_METADATA/.

We can copy mostly verbatim the macros from systemd codebase.

Example output:

	$ meson setup --native-file build-dev.ini -Dxz=disabled -Ddlopen=zlib build
	...
	    dlopen           : zlib

	    features         : +ZSTD -XZ +ZLIB +OPENSSL

	$ dlopen-notes.py build/libkmod.so.2
	# build/libkmod.so.2
	[
	  {
	    "feature": "xz",
	    "description": "Support for uncompressing xz-compressed modules",
	    "priority": "recommended",
	    "soname": [
	      "liblzma.so.5"
	    ]
	  }
	]

Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/262