i965/nir/fs: Implement nir_intrinsic_load_ssbo
i965/nir/fs: Implement nir_intrinsic_load_ssbo

Reviewed-by: Kristian Høgsberg <ca9b5b1e27d4fa7f4ba6848bdd08ca52cfd6330c@bitplanet.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler