radv/winsys: Expand scope of allbos lock.

radv/winsys: Expand scope of allbos lock.

With us not creating a bo_list anymore, there is a problem if we
delete a buffer between enumerating all buffers and doing the submission.

Also changes this to a rwlock given the wider scope of the things under
lock. (especialy some of the syncobj stuff is now under the lock)

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7091>