MIPS: Octeon: Define ARCH_HAS_USABLE_BUILTIN_POPCOUNT for OCTEON.

OCTEON implements __builtin_popcount with a single instruction, so lets use it.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Cc: David Daney <ddaney@caviumnetworks.com>
Patchwork: https://patchwork.linux-mips.org/patch/1431/


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