i965: Directly call intel_batchbuffer_flush() after i915 split.

i965: Directly call intel_batchbuffer_flush() after i915 split.

intel_flush() now did nothing except call through (and
intel_batchbuffer_flush() does the no-op check, too!)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>