MIPS: Octeon: Remove vestiges of CONFIG_CAVIUM_OCTEON_2ND_KERNEL

MIPS: Octeon: Remove vestiges of CONFIG_CAVIUM_OCTEON_2ND_KERNEL

This config option never really worked, and has bit-rotted to the
point of being completely useless.  Remove it completely.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Steven J. Hill <steven.hill@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15314/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>