nir/spirv: initial handling of OpenCL.std extension opcodes

nir/spirv: initial handling of OpenCL.std extension opcodes

Not complete, mostly just adding things as I encounter them in CTS. But
not getting far enough yet to hit most of the OpenCL.std instructions.

Anyway, this is better than nothing and covers the most common builtins.

v2: add hadd proof from Jason
    move some of the lowering into opt_algebraic and create new nir opcodes
    simplify nextafter lowering
    fix normalize lowering for inf
    rework upsample to use nir_pack_bits
    add missing files to build systems
v3: split lines of iadd/sub_sat expressions

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>