i965 Gen4/5: Introduce 'interpolation map' alongside the VUE map

i965 Gen4/5: Introduce 'interpolation map' alongside the VUE map

The interpolation map (in brw->interpolation_mode) is a new auxiliary
structure alongside the post-GS VUE map, which describes the
interpolation modes for each VUE slot, for use by the clip and SF
stages.

This patch introduces a new state atom to compute the interpolation map,
and adjusts the program keys for the clip and SF stages, but it is not
actually used yet.

[V1-2]: Signed-off-by: Olivier Galibert <galibert at pobox.com>

V3: Updated for vue_map changes, intel -> brw merge, etc. (Chris Forbes)
V4: Compute interpolation map as a new state atom rather than tacking it
on the front of the clip setup
V5: Rework commit message, make interpolation_mode_map a struct.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>