radeonsi: set up IBs for preemption

- Execute cs_preamble_state as a separate IB with different flags.
- Set the PREEMPT flag for the main IB.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5798>
4 files changed