i965: Enable cross-thread constants and compact local IDs for hsw+

i965: Enable cross-thread constants and compact local IDs for hsw+

The cross thread constant support appears on Haswell. It allows us to
upload a set of uniform data for all threads without duplicating it
per thread.

One complication is that cross-thread constants are loaded into
registers before per-thread constants. Previously, our local IDs were
loaded before the uniform data and treated as 'payload' data, even
though they were actually pushed into the registers like the other
uniform data.

Therefore, in this patch we simultaneously enable a newer layout where
each thread now uses a single uniform slot for a unique local ID for
the thread. This uniform is handled specially to make sure it is added
last into the uniform push constant registers. This minimizes our
usage of push constant registers, and maximizes our ability to use
cross-thread constants for registers.

To swap from the old to the new layout, we also need to flip some
lowering pass switches to let our driver handle the lowering instead.
We also no longer force thread_local_id_index to -1.

v4:
 * Minimize size of patch that switches from the old local ID layout
   to the new layout (Jason)

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>