Add a new backend for any character device. This backend uses channel
in spice connection. This channel is similar to spicevmc, but
all-purpose in contrast to spicevmc.
Apart from spicevmc, spiceport-backed chardev will not be formatted
into the command-line if there is no spice to use (with test for that
as well). For this I moved the def->graphics counting to the start
of the function so its results can be used in rest of the code even in
the future.
Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
