i965: Make brw_compute_vue_map's userclip dependency a boolean.

i965: Make brw_compute_vue_map's userclip dependency a boolean.

Previously, brw_compute_vue_map required an argument indicating the
number of clip planes in use, but all it did with it was check if it
was nonzero.

This patch changes brw_compute_vue_map to take a boolean instead.
This allows us to avoid some unnecessary recompilation of the Gen4/5
GS and SF threads.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>