The support for multiple serial interfaces as implemented is mainly
  intended to allow for modem dial-in / dial-out while still being able
  to use a serial console on a (different) serial port.

  MPC8XX Specific
  ===============

  At the moment, the ports must be split on a SMC and a SCC port  on  a
  8xx processor; other configurations are not (yet) supported.
  
  Support for hardware handshake has not been implemented yet (but is
  in the works).
  
  *) The default console depends on the keys pressed:
  	- SMC if keys not pressed (modem not enabled)
  	- SCC if keys pressed (modem enabled)
  
  *) The console can be switched to SCC by any of the following commands:
  
  	setenv stdout serial_scc
  	setenv stdin serial_scc
  	setenv stderr serial_scc
  
  *) The console can be switched to SMC by any of the following commands:
  
  	setenv stdout serial_smc
  	setenv stdin serial_smc
  	setenv stderr serial_smc
  
  *) If a file descriptor is set to "serial" then the current serial device
  will be used which, in turn, can be switched by above commands.
  
  *) The baudrate is the same for all serial devices. But it can be switched
  just after switching the console:
  
  	setenv sout serial_scc; setenv baudrate 38400
  
  After that press 'enter' at the SCC console. Note that baudrates <38400

  are not allowed on LWMON with watchdog enabled (see CONFIG_SYS_BAUDRATE_TABLE in

  include/configs/lwmon.h).

  
  
  PPC4XX Specific
  ===============
  *) The default console is UART0
  
  *) The console can be switched to UART1 by any of the following commands:
  	setenv stdout serial1
  	setenv stderr serial1
  	setenv stdin serial1
  
  *) The console can be switched to UART0 by any of the following commands:
  	setenv stdout serial0
  	setenv stderr serial0
  	setenv stdin serial0