MIPS: Netlogic: Make number of nodes configurable

There can be 1, 2 or 4 SoCs(nodes) in a multi-chip XLP board. Add an
option for multi-chip boards in case of XLP, and make the number of
nodes configurable.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Patchwork: http://patchwork.linux-mips.org/patch/4470
Signed-off-by: John Crispin <blogic@openwrt.org>