radv/winsys: Fail early on overgrown cs.
When !use_ib_bos, we can't easily chain ibs one to another. If the
required cs size grows over 1Mi - 8 dwords just fail the cs so that we
won't assert-fail in radv_amdgpu_winsys_cs_submit later on.
Reviewed-by:
Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>