dgnc: get rid of dpacompat.h, move remaining stuff to digi.h

Dpacompat.h contained a lot of unused #defines and only few things are
used from it so since we've trimmed down digi.h, now we can delete
dpacompat.h and move remaining stuff into digi.h.

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>