i965: Store absolute thread count in max_wm_threads on Broadwell.

i965: Store absolute thread count in max_wm_threads on Broadwell.

In the past, 3DSTATE_PS took an absolute number of threads.  Conversely,
on Broadwell you always program 64, and it implicitly scales based on
the GT-level with no special programming.  So, I stored 64 in
brw_device_info::max_wm_threads.

However, I didn't realize that we also use max_wm_threads to compute the
size of the scratch space buffer.  In that case, we really need the
absolute number of threads.

This patch hardcodes 3DSTATE_PS to use the value it expects, and changes
max_wm_threads back to a (completely fake) absolute thread count (once
again copied from Haswell).

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