Documentation: replace install commands with softdeps

Install commands should not be used to specify soft dependencies among
modules. When loading modules it's much better to have a softdep that
modprobe knows what's being done than having to fork/exec another
instance of modprobe to load the other module.

By using a softdep user has also an option to remove the dependencies
when removing the module (and if its refcount dropped to 0)

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>