i965: Stop re-uploading push constants after URB reconfiguration.

i965: Stop re-uploading push constants after URB reconfiguration.

Previously we would re-upload the constant data to the batchbuffer,
then re-emit the packets.  We only need to do the last step (causing
the existing data in the batchbuffer to be re-uploaded to the push
constant staging area in the L3).

Now that we've separated the two, it's pretty easy to accomplish.

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