package/lz4: make program installation optional

Often lz4 is used as a library, and not as a standalone program.
Excluding lz4 binary will save some space in this case. Indeed, the
lz4 program is always statically linked against its library, which
makes it duplicate the whole library size:

$ ls -l usr/lib/liblz4.so.1.9.2 usr/bin/lz4
-rwxr-xr-x 1 thomas thomas 226724 27 juil. 16:33 usr/bin/lz4
-rwxr-xr-x 1 thomas thomas 156996 27 juil. 16:33 usr/lib/liblz4.so.1.9.2

Since lz4 is now primarily a library, it's moved to the "Libraries"
section.

Of course, installation of programs defaults to "yes" to preserve
backward compatibility.

Signed-off-by: Ed Spiridonov <edo.rus@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>