radv: Avoid deadlock on bo_list.

radv: Avoid deadlock on bo_list.

With the kernel timeline sysncobj changes, the kernel submits do
not necessarily happen in global vkQueueSubmit order. Which should
be fine, we added the appropriate waits for that. (See
DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT in the winsys)

However, all kernel submissions take a lock on the bo_list mutex,
and since we do the wait in the winsys, we wait while having the
bo_list mutex held. This means that as soon as a wait and a signal
submission are out of order we have a deadlock on the bo_list mutex
and the wait.

Solution is to use a shared reader lock during the kernel submission,
as we only need read access for the submission.

Fixes: 6bc5ce7a91d "radv: Add timeline syncobj for timeline semaphores."
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3446
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6478>