MIPS: Netlogic: Avoid unnecessary cache flushes

XLR dcache is fully coherent across CPUs, so avoid unnecessary dcache
flushes.

Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2729/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>