MIPS: IP27: Fix __node_distances undefined error

export the __node_distances symbol in the ip27 memory code to fix the
build error:

  Building modules, stage 2.
  MODPOST 311 modules
ERROR: "__node_distances" [drivers/block/nvme.ko] undefined!
scripts/Makefile.modpost:90: recipe for target '__modpost' failed

when building the kernel with:
 CONFIG_SGI_IP27=y
 CONFIG_BLK_DEV_NVME=m

Signed-off-by: James Cowgill <James.Cowgill@imgtec.com>
Cc: <stable@vger.kernel.org> # v3.15+
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>