MIPS: Netlogic: Move serial ports to device tree

Add the serial ports to the device tree and remove the platform
code for adding them.

Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
Patchwork: http://patchwork.linux-mips.org/patch/4098/


Signed-off-by: John Crispin <blogic@openwrt.org>