i965/hsw: Implement end of batch workaround

i965/hsw: Implement end of batch workaround

This patch can cause an infinite recursion if the previous patch titled, "i965:
Track finished batch state" isn't present (backporters take notice).

v2: Sent out the wrong patch originally. This patches switches the order of
flushes, doing the generic flush before the CC_STATE, and the required
workaround flush afterwards

v3: Only perform workaround for render ring
Add text to the BATCH_RESERVE comments

v4 (By Ken): Rebase; update citation to mention PRM and Wa name; combine two
blocks.

http://otc-mesa-ci.jf.intel.com/job/bwidawsk/171/

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>