i965: Separate uploading push constant data from the pointer packets.

i965: Separate uploading push constant data from the pointer packets.

I hope to upload UBO via 3DSTATE_CONSTANT_XS packets, in addition to
normal uniforms.  In order to do that, I'll need to re-emit the packets
when UBOs change.  But I don't want to re-copy the regular uniform data
to the batchbuffer every time.

This patch separates out the data uploading from the packet submission.
We're running low on dirty bits, so I made the new atom happen on every
draw call, and added a flag to stage_state indicating that we want the
packet for that stage emitted.

I would have preferred to do this outside the atom system, but it has
to happen between the uploading of push constant data and the binding
table upload.

Reviewed-by: Matt Turner <mattst88@gmail.com>