anv: Improve BTI change cache flushing

anv: Improve BTI change cache flushing

This commit makes two changes:

 1. We set pending_pipe_bits instead of emitting PIPE_CONTROL directly
    for the flush at the end of cmd_buffer_begin_subpass.

 2. Because BLORP ops such as vkCmdClearAttachments may come in the
    middle of a render pass, we have to also flag the need for a cache
    flush after the blorp op.

Fixes: 185630c6bc97 "anv/blorp: Do the gen11 BTI flush"
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3547>