winsys/amdgpu: pass PIPE_CONTEXT_* flags to ctx_create

instead of using our own flags; also REALTIME_PRIORITY is never used,
so the relevant code is removed

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34983>
8 files changed