Blackfin: jtag-console: add debug markers

While we're in here, add some useful debug points.  We need custom debug
statements because we need the output to only go to the serial port.  If
we used the standard debug helpers, the output would also go to the stdout
(which would be the jtag console) and make it hard to figure out what is
going where exactly.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>