v3dv/cmd_buffer: cache viewport translate/scale

Before that commit we were calling get_viewport_xform to get those
values twice (to emit scissor and viewport), and we found that we
would need that info even more times. So let's just compute that info
when setting the viewport, and reuse the values.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>
2 files changed