MIPS: Don't build fast TLB refill handler with 32-bit kernels

The fast handler only supports 64-bit kernels.

Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Cc: James Hogan <james.hogan@imgtec.com>
Cc: kvm@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7010/


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