i965: Add CS push constant info to brw_cs_prog_data

i965: Add CS push constant info to brw_cs_prog_data

We need information about push constants in a few places for the GL
driver, and another couple places for the vulkan driver.

When we add support for uploading both a common (cross-thread) set of
push constants, combined with the previous per-thread push constant
data, things are going to get even more complicated. To simplify
things, we add push constant info into the cs prog_data struct.

The cross-thread constant support is added as of Haswell. To support
it we need to make sure all push constants with uniform values are
added to earlier registers. The register that varies per thread and
holds the thread invocation's unique local ID needs to be added last.

For now we add the code that would calculate cross-thread constatn
information for hsw+, but we force it (cross_thread_supported) off
until the other parts of the driver support it.

v4:
 * Support older local ID push constant layout as well. (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>