MIPS: octeon: Remove cpu_has_saa

The cpu_has_saa feature macro was added along with Cavium Octeon CPU
support back in commit 5b3b1688 ("MIPS: Add Cavium OCTEON processor
support files to arch/mips/cavium-octeon.") but has never been used.

Remove the dead code.

Signed-off-by: Paul Burton <paul.burton@mips.com>