staging: comedi: das08: Mark 'JR' boards in board data

Add a bool member `is_jr` to `struct das08_board_struct` and initialize
it to `true` in those elements of `das08_boards[]` corresponding to the
'JR' board models.  This will be used by a following patch that removes
the `ai`, `ao`, `di` and `do` members from `struct das08_board_struct`.

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