i965: Cope with batch getting flushed in the middle of batchbuffer emits.

i965: Cope with batch getting flushed in the middle of batchbuffer emits.

This isn't required for GEM (at least, yet), but the check_aperture code
for non-GEM results in batch getting flushed during emit.  brw_state_upload
restarts state emits, but a bunch of the state emit functions were assuming
that they would be called exactly once, after prepare and before new_batch.

Bug #17179.