system: update Config.in comment about systemd dependencies

system: update Config.in comment about systemd dependencies

In commit 879fa7f82a86ffdc6d1cf7c9bfbb5cf830583d69, the
BR2_INIT_SYSTEMD option was changed to allow selecting with a uClibc
toolchain. Unfortunately, the corresponding Config.in comment, which
was already bogus, was not updated to take into account the numerous
dependencies of BR2_INIT_SYSTEMD.

Due to this, even if you have uClibc enabled, the BR2_INIT_SYSTEMD
option may not be visible, and the Config.in comment may also not be
visible, leaving the user in the dark.

This commit fixes the dependencies of the Config.in comment so that
they match the one of the BR2_INIT_SYSTEMD option.

Reported-by: Raphael Jacob <r.jacob2002@gmail.com>
Cc: Raphael Jacob <r.jacob2002@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>