freedreno/a6xx: Build up draw dword0 outside visibilty if statement

freedreno/a6xx: Build up draw dword0 outside visibilty if statement

Pulling this logic out means we can share the logic and avoid a couple
of temporary variables that helped make things clearer before. Note
that in either vismode case, we always program vismode 0.

Signed-off-by: Kristian H. Kristensen <hoegsberg@chromium.org>