Blackfin Serial Driver: Enable IR function when user application (irattach...

Blackfin Serial Driver: Enable IR function when user application (irattach /dev/ttyBFx -s) call TIOCSETD ioctl with line discipline N_IRDA

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>