i965: Implement selection of the closest L3 configuration based on a vector of weights.

i965: Implement selection of the closest L3 configuration based on a vector of weights.

The input of the L3 set-up code is a vector giving the approximate
desired relative size of each partition.  This implements logic to
compare the input vector against the table of validated configurations
for the device and pick the closest compatible one.

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Kristian Høgsberg  <krh@bitplanet.net>