i965: Explicitly write the "TR DS Cache Disable" bit at TCS EOT.

i965: Explicitly write the "TR DS Cache Disable" bit at TCS EOT.

Bit 0 of the Patch Header is "TR DS Cache Disable".  Setting that bit
disables the DS Cache for tessellator-output topologies resulting in
stitch-transition regions (but leaves it enabled for other cases).

We probably shouldn't leave this to chance - the URB could contain
garbage - which could result in the cache randomly being turned on
or off.

This patch makes the final EOT write 0 to the first DWord (which
only contains this one bit).  This ensures the cache is always on.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>