hvc: add Blackfin JTAG console support

This converts the existing bfin_jtag_comm TTY driver to the HVC layer so
that the common HVC code can worry about all of the TTY/polling crap and
leave the Blackfin code to worry about the Blackfin bits.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>