vk/pipeline: Track VB's that are actually used by the pipeline

vk/pipeline: Track VB's that are actually used by the pipeline

Previously, we just blasted out whatever VB's we had marked as "dirty"
regardless of which ones were used by the pipeline.  Given that the stride
of the VB is embedded in the pipeline this can cause problems.  One problem
is if the pipeline doesn't use the given VB binding we emit a bogus stride.
Another problem is that we weren't properly resetting the dirty bits when
the pipeline changed.