MIPS: Octeon: Allow CVMSEG to be disabled

Don't include cvmseg states into thread_status when
CONFIG_CAVIUM_OCTEON_CVMSEG_SIZE is not defined or 0.

Fix compile for kernel without this feature.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>