i965/nir/vec4: Implement load_uniform intrinsic
i965/nir/vec4: Implement load_uniform intrinsic

For the indirect case we need to take the index delivered by
NIR and compute the parent uniform that we are accessing (the one
that we uploaded to a surface) and the constant offset into that
surface.

Reviewed-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler