s390/con3270: generate status line during output

Updating the status line is almost the same as generating
it when redrawing the screen. However, the code is much easier
to read when doing so.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>