This avoids SIMD-optimized functions having to sign-extend their
line size argument manually to be able to do pointer arithmetic.
Also adjust parameter names to be "stride" everywhere.
Silence a warning due to frame assignment in dvenc. All uses of the
reference in dvdec are read only, except the ones in the main decoding
function, so use the frame pointer directly there.
This is necessary to avoid target config settings bleeding into the host
compilation process with hardcoded tables and the DV VLC tables no longer
present as static tables in a header file.
