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.
This changes the way descriptor sets and layouts work so that we fill
out binding table contents at the time we bind descriptor sets. We
manipulate the binding table contents and sampler state in a shadow-copy
in anv_cmd_buffer. At draw time, we allocate the actual binding table
and sampler state and flush the anv_cmd_buffer copies.
This way we can pass in a vertex shader and yet have the pipeline emit an
empty 3DSTATE_VS packet. We need this for meta because we need to trick
the compiler into not deleting our inputs but at the same time disable the
VS so that we can use a rectlist. This should go away once we actually get
SPIR-V.
