v3d: include offset as part of streamout target

v3d: include offset as part of streamout target

When dealing with multiple Transform Feedback buffers, each of them
needs to have their own offset, so when resuming from one to another we
know exactly were to continue adding primitives.

Fixes "spec@arb_transform_feedback2@change objects while paused (gles3)"
piglit test.

Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17373>