i965: Mark TCS URB writes as having side effects.

i965: Mark TCS URB writes as having side effects.

This adds barrier dependencies around TCS_OPCODE_URB_WRITE, preventing
reads and writes from being incorrectly scheduled.

Fixes rendering in GFXBench 4.0's tessellation demo.

For some reason, we haven't ever listed URB writes as having
side-effects.  This hasn't been a problem because in most stages, we
never read from the URB, and only write to each location once.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93526
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>