MIPS/OCTEON: Override default address space layout.

OCTEON II cannot execute code in the default CAC_BASE space, so we
supply a value (0x8000000000000000) that does work.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5457/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>