st/glsl_to_nir: disable io lowering to temps for tess

st/glsl_to_nir: disable io lowering to temps for tess

Lowering these to temps makes a big mess, and results in some
piglit test failures. Also the radeonsi backend (the only backend
to support tess) has support for indirects so there is no need to
lower them anyway.

Fixes the following piglit tests on radeonsi:

tests/spec/arb_tessellation_shader/execution/variable-indexing/tes-input-array-vec3-index-rd.shader_test
tests/spec/arb_tessellation_shader/execution/variable-indexing/tes-input-array-vec4-index-rd.shader_test

Reviewed-by: Marek Olšák <marek.olsak@amd.com>