RSC and LOM devices have fixed speed settings.

We already had some code to match and handle "rsc" named devices on
E250 systems, but we also have to handle 'rsc-console', 'rsc-control',
and 'lom-console'.

Also, in order to get this right regardless of what 'output-device'
happens to be, explicitly pass the UART device node pointer to this
routine.
Signed-off-by: David S. Miller <davem@davemloft.net>