meson.build: install kmod symlinks to /usr/sbin/

meson.build: install kmod symlinks to /usr/sbin/

With earlier commit we added support for kmod itself to install the
symlinks to kmod. While it works across the board, some distributions
still support (to varying degree) split /usr/bin and /usr/sbin.

This commit changes the location where those are created and bears no
functional change for merged bin-sbin users. While for split ones, it
follows what distributions are doing to a varying extend:

 - Fedora, Alpine - this commit matches exactly what they do
 - Debian, Yocto - they have an extra /bin/lsmod -> ../sbin/kmod symlink
 - Gentoo - as Debian plus an extra /bin/modinfo -> ../sbin/kmod symlink

Loosely based on a Debian patch by Marco d'Itri.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/231
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>