m68knommu: add missing interrupt line definition for UART 2

Signed-off-by: David Wu <david.wu@arcturusnetworks.com>
Acked-by: Michael Durrant <mdurrant@arcturusnetworks.com>
Acked-by: Oleksandr Zhadan <oleks@arcturusnetworks.com>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>