Trivial code simplification
Add missing const
Fix DOT4 missing from getTargetOpcodeName
R600: Make check clearer.

The check is clearer as southern islands or later,
rather than checking for later than northern islands.
R600/SI - Add new CI arithmetic instructions.

Does not yet include larger part required
to match v_mad_i64_i32 / v_mad_u64_u32.