[mips] Add Octeon cnMips instructions seqi/snei and v3mulu/vmm0/vmulu.

This patch adds the Octeon cnMips instructions seqi/snei and v3mulu/vmm0/vmulu.
It is only for the assembler. Test case is included.

Reviewed by: Daniel.Sanders@imgtec.com

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205631 91177308-0d34-0410-b5e6-96231b3b80d8