i965: Initial Ivybridge URB space partitioning, including push constants.

i965: Initial Ivybridge URB space partitioning, including push constants.

Currently this always reserves 16kB for push constants, regardless of
how much space is needed, and partitions it evenly betwen the VS and FS.
This is probably not ideal, but is straightforward.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>