MIPS: Use 64-bit stores to c0_entrylo on 64-bit kernels.

64-bit CPUs have 64-bit c0_entrylo{0,1} registers.  We should use the
64-bit dmtc0 instruction to set them.  This becomes important if we
want to set the RI and XI bits present in some processors.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/954/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>