i965: Split shader_time entries into separate cachelines.

i965: Split shader_time entries into separate cachelines.

This avoids some snooping overhead between EUs processing separate shaders
(so VS versus FS).

Improves performance of a minecraft trace with shader_time by 28.9% +/-
18.3% (n=7), and performance of my old GLSL demo by 93.7% +/- 0.8% (n=4).

v2: Add a define for the stride with a comment explaining its units and
    why.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>