Blackfin Serial Driver: Fix bug - ircp fails on sir over Blackfin UART

We now use the sir_dev/irtty_sir/uart/bfin_serial drivers framework
to monitor the TX status.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>