i965/blorp: Use 8k chunk size for urb allocation

i965/blorp: Use 8k chunk size for urb allocation

Previously, we hardcoded "VS URB Starting Address" to 2 (in 8kB chunks),
which meant VS URB data would start at an offset of 16kB.

However, on Haswell GT3 and Gen8+, we allocate the first 32kB for the
push constant region.  This means that the PS push constant and VS URB
data regions overlap, which can lead to corruption.

v2 (Ken): Better description of the change, and do not change vs_size
          from 2 to 1.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>