anv: Rework vkCmdPipelineBarrier()

anv: Rework vkCmdPipelineBarrier()

We don't need to look at the stage flags, as we don't really support any
fine-grained, stage-level synchronization. We have to do two
PIPE_CONTROLs in case we're both flushing and
invalidating.

Additionally, if we do end up doing two PIPE_CONTROLs, the first,
flusing one also has to stall and wait for the flushing to finish, so we
don't re-dirty the caches with in-flight rendering after the second
PIPE_CONTROL invalidates.