MIPS: Netlogic: L1D cacheflush before thread enable on XLPII

On XLPII CPUs, the L1D cache has to be flushed with regular cache
operations before enabling threads in a core.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6276/