staging: comedi: Kconfig: make COMEDI_BOND select COMEDI_KCOMEDILIB

Currently, to select the "comedi_bond" driver, the "kcomedilib" support
has to be selected first.  It seems more natural to allow the
"comedi_bond" driver to be selected on its own and to automatically
select the "kcomedilib" module as a result of that.  Change the
dependency/select relationship between the two configuration options to
do that.

Also, make "kcomedilib" a module that can be selected independently,
perhaps for use by out-of-tree modules, although it is not terribly
useful for anything other than "comedi_bond" currently.

Also, improve the help text for the config options.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>