i965/blorp: Bump the batch space estimate

i965/blorp: Bump the batch space estimate

Commit f938354362655a378d474c5f79c52cea9852ab91 recently increased the
alignment on vertex buffer data from 32 to 64.  This caused us to
consume a bit more batch than we were before and we now go over the
estimate by a small amount on certain blits on gen8+.  This commit bumps
then gen8 batch estimate by a bit to compensate.  Haswell and older
still seems to be well within the limit.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100582
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "13.0 17.0" <mesa-stable@lists.freedesktop.org>