radv: Move normal (non-empty) queue submit to a separate function.

radv: Move normal (non-empty) queue submit to a separate function.

Also move the preamble update into this function, as that is only needed
by this code path and not needed for empty submits.

With this change, the goal is to make radv_queue_submit easier to
read and understand. This prepares it for future work when we'll
add the capability to submit to multiple queues at the same time.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-By: Tatsuyuki Ishi <ishitatsuyuki@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16358>