staging: dgnc: Move utility functions out of dgnc_driver.c

This commit moves the utility functions out of dgnc_driver.c file and
puts them in the new dgnc_utils.{c,h} files. The accompanying changes
adjust the existing code to work with this design.

Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>