i965: Rework brw_new_batch to actually start a new batch.

i965: Rework brw_new_batch to actually start a new batch.

Previously, brw_new_batch was called just after execbuf, but before
intel_batchbuffer_reset.  Essentially, it prepared for the creation of a
new batch, that wasn't yet available, and which it didn't create.  This
was a bit awkward.

This patch makes brw_new_batch call intel_batchbuffer_reset as the very
first operation.  This means that brw_new_batch actually creates a new
batchbuffer, and thus has it available.  It brings the creation of the
new batchbuffer and BRW_NEW_BATCH flagging together into one place.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>