MIPS: Netlogic: Split XLP L1 i-cache among threads

Since we now use r4k cache code for Netlogic XLP, it is
better to split L1 icache among the active threads, so that
threads won't step on each other while flushing icache.

The L1 dcache is already split among the threads in the core.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Patchwork: http://patchwork.linux-mips.org/patch/4787/
Signed-off-by: John Crispin <blogic@openwrt.org>